NATIONAL DEFENSE RESEARCH COMMITTEE
REPORT NO. A-9O : PROGRESS REPORT
THE EROSION OF GUNS
Part One: Fundamentals of Ordnance
Relating to Gun Erosion
by
John S, Burlew
Approved on September G, 19h2
for submission to the Section Chairman
Approved on September 8, 1?42
for submission to the Division Chairman
Approved on September 9, 19h2
for submission to the Committee
hn S. Burlew, Consultant
Section A, Division A
L. H. Adams, Chaiman
Section A, Division A
z6
Richard 0, Tolman, Chairman
Division A
Preface
The work described in this report is pertinent to the pro-
ject designated by the War Department Liaison Officer as OD-52,
to the project designated by the Navy Department Liaison Officer
as NO-23 and to Division A projects PA-230 and РА-2ЦО.
Part of the work of preparation of this report was perform-
ed under Contract OEMsr-51 with the Carnegie Institution of
Washington and elsewhere under the auspices of Section A.
Through arrangements made in July, 19h1 with Brigadier
General R. H, Somers, then Ordnance Department Liaison Officer
with the National Defense Research Committee, the writer was
given access to the confidential reports of the Ordnance Depart-
ment dealing with gun erosion, for the purpose of preparing this
report. The information gained during several months of work in
the Ordnance Department Technical Library was supplemented by
discussions with both officers and civilian personnel of the War
and Navy Departments.
This report has been issued in two volumes. The present
volume comprises Part One, on the fundamentals of ordnance relat-
ing to gun erosion. The second volume will comprise Part Two, on
the characteristics of gun erosion, A bibliography and an author
index appears in each volume, but the subject index appears only
at the end of the second volume.
Acknowledgements. — The writer is grateful for the friendly
cooperation of the many persons who assisted him in gathering in-
formation. He is especially indebted to Mr. S, Faitman, Principal
Ordnance Engineer of the Ballistic Section of the Technical Divi-
sion, Industrial Service, Ordnance Department, who was a friendly
mentor in matters of ordnance, to Mrs, S. H. Pendleton and her
assistants in the Ordnance Department Technical Library, and to
Mrs. R. E. Gibson, who helped collect data and who prepared the
manuscript.
Distribution of copies of the report. — The editorial staff
of Division A completed preparation of this report for duplication
on September 15, 19^2. The initial distribution of copies was as
follows:
Copies No. 1 to 2li, inclusive, to the Office of the Secretary
of the Committee for distribution in the usual manner;
Copies No, 25 to 33, inclusive to the Chief of Ordnance, War
Department (Attention: Col. W. R. Gcarhardt# Col, S. B. Ritchie,
Col. R. R. Studler (2 copies), Lt, Col. D, J. Martin, Capt. С. E.
Balleisen, S< Feltman, P. M. Netzer, Technical Library);
iii
Copies No. Jli to 36, inclusive, to Aberdeen Proving Ground
(Attention; Lt. Col. L. E, Simon, R. H. Kent, J. R. Lane);
Copies No, 37 to hO, inclusive, to Watertovm. Arsenal (Atten-
tion: Col. H. H. Zornig (2 copies), P. R. Kosting, H. H. Lester);
Copy No. 111 to Watervliet Arsenal (Attention: Lt. Col. 3» L.
Conner); ,
Copy No. h-2 to Frankford Arsenal (Attention: Lt. Col. L. S.
Fletcher);
Copy No. 113 to Springfield Armory (Attention: Capt. A. E*
Benson);
Copies No. hb to I16, inclusive to the Chief of the Bureau
of Ordnance, Navy Department (Attention: Capt. G. L. Schuyler,
Lt. B. D. Hills, С. B. Green);
Copy No. 117 to the Office of the Coordinator of Research,
Navy Department (Attention: Lt. T. C. Wilson);
Copy No. L18 to the Naval Research Laboratory (Attention:
R. Gunn);
Copy No. to the Inspector of ordnance in charge, Naval
Proving Ground, Dahlgren, Va.
Copy No. 50 to С. C. Lauritsen, Vice Chairman, Division A;
Copies No. S1 to 60, inclusive, to L. H, Adams, Chairman
Section A, Division A;
Copy No. 61 to H. B. Allen, Vice Chairman, Section A,
Division A;
Copy No. 62 to L. J. Briggs, Member, Section A, Division A;
Copies No. 63 and 6Lt to E. L. Rose, Member, Section A,
Division A;
Copy No.	65	to	E.	R.	tfeidlein, Member, Section A, Division A;
Copy No.	66	to	J.	S.	Burlaw,	Consultant,	Section	A,	Division	A;
Copy No.	67	to	H.	L.	Curtis,	Consultant,	Section	A,	Division	A;
Copy No.	6S	to	R.	E.	Gibson,	Consultant,	Section	A,	Division	A;
Copy No. 69 to W, F. Jackson, Consultant, Section A, Division A;
iv
Copy No. ?0 to J. F. Kincaid, Consultant^ Section A, Division A$
Copy No. 71 to T. C. Poultor, Consultant, Section A, Division Aj
Copy No. 72 to J. Wulff, Consultant, Section A, Division A;
Copy No, 73 to J. 0. Hirschfelder, Consultant, Section A,
Division A;
Copy No. to P. Bridgman, Consultant, Section B, Division A;
Copy No. 75 to G. B. Kistiakowsky, Chairman, Section B-1,
Division B;
Copies No. 76 to 80, inclusive, to the Secretary of the Committee
for transmittal to L. C. Pauling, Clyde Williams, J. C. W. Frazer,
I. M. Stein, J, P,' ilagos.
v
CONTENTS
Pj'JIT ONE
FUNDAMENTALS OF ORDNANCE RELATING TO GUN EROSION
Chapter	Page
Foreword by L.	H. Adams .......................... ix
I.	Introduction ....................................... 1
II.	Guns ............................................... 7
III.	Projectiles ....................................... 26
TV	.	Propellants ....................................... 33
.	V.	Burning of the	Powder ........................... Ц2
VI,	Movement of the Projectile in the Bore .......♦	69
VII.	Reaction of the Tube to Firing .................... 79
Bibliography and Author Index for Part One ..	89
PART TWO*
THE CHARACTERISTICS	OF	GUN	EROSION
VIII»	Magnitude of Erosion
IX.	The Eroded Surface
X.	Experimental Methods	of	Study	of	Gun	Erosion
XI.	Relation Between Properties of the Gun Metal and
Erosion
XII.	Conditions of Firing that Influence the Rate of
Erosion
XIII.	Effect on Erosion of Leakage of Gas Past the
Projectile
XTV.	Life of Guns
XV.	Theories of the Mechanism of Erosion
Bibliography and author Index for Part Two
Subject Index to Parts One and Two
Part Two appears in a second volume designated as NDRC
Report A-91.
vii
foreword
By L. H., Adams
Shortly after Section A of Division д was constituted for the
purpose of attacking the problem “of gun erosion and other aspects
of hyper-velocity, and the facilities of the Geophysical Labora-
tory of the Carnegie Institution of Washington were made avail-
able for this work, Dr. John S. Burlew of the scientific staff of
that laboratory was requested to prepare a report on gun erosion.
It was realized that there existed a vast amount of factual mate-
rial in this field and a large number of conflicting interpreta-
tions and conclusions relating to the observations. The intention
was to have an outline of the subject that would be comprehensive
but not necessarily exhaustive, and to include merely a cross-
section of existing data together with an explanation of the terms
used and a summary of the conclusions that have been drawn. Col-
lecting and assembling the necessary information was a task of
considerable magnitude, which would have been even greater but for
the hearty cooperation and encouragement of various individuals in
the Army and Navy and in other organizations.
The purpose of the report has been to provide the necessary
ground work for planning investigations on the mechanism of gun
erosion. A considerable portion of it has been available for some
time to me and to other persons working on this problem. The pro-
gram was first presented and discussed at the Conference on Gun
Erosion held at Watertown ^rsenal on October 1?, 19Ш, at which
ix
representatives of the National Defense Research Committee as well
as of various establishments of the Army and Navy were present»
Since then the investigation of the mechanism of gun erosion has
been going forward actively at the Geophysical Laboratory and else-
where under the auspices of Section A. The present report, which
in its completed form provides a convenient background for these
investigations, does not include any of the results already obtain-
ed in them. Those results arc being presented in a scries of
Division A memorandums and reports, the first few of which have
already been issued or are in preparation, as mentioned in foot-
notes to the appropriate parts of the text of the present report.
Washington, D. C.
August 11, 1?h2.
THE EROSION OF GUNS
Part One: Fundamentals of Ordnance
Relating to Gun Erosion’
CHAPTER I. INTRODUCTION
1.	The present survey of the erosion of guns aims to collate the
principal factual data on the subject and, in addition, to summarize
the different theories that have been proposed to explain or to cor-
relate these facts. Special care has been exercised to separate the
facts from the various interpretations that may be placed upon them,
since the latter in many instances depend on unverified assumptions.
The sources of all information have been indicated in order that the
reader may consult them for further details; for, although this sur-
vey attempts to be comprehensive, the treatment of the various items
mentioned is not intended to be exhaustive.
2.	Definitions
A gun consists essentially of a hollow metal tube having' one
end — the breech — tightly closed and having within it a projectile
that is expelled with a high velocity from the open muzzle by the
rapid expansion of the gases which are formed by the burning of the
propellent powder placed in the chamber behind the projectile before
firing. Erosion of a gun is the gradual removal of metal from the
surface of the bore of the tube as a result of firing. It has been
suggested that it is desirable to distinguish between the ’’erosion”
caused by the hot powder gases and the mechanical "wear” caused by
- 2 -
the movement of the projectile; but there is not yet enough evidence
1/
to permit this distinction.-7 Hence in the present discussion the
inclusive term erosion will be used to refer to enlargement of the
bore without implication as to the cause.
This enlargement of the bore radically affects the flight of
the projectile. Erosion at the breech end of the tube decreases the
range of the gun, and erosion at both ends decreases its accuracy.
The two effects combine to determine the useful life of the gun.
Some of the methods of estimating the life of guns from the extent
of erosion are treated in Chap. XIV.
3.	High muzzle velocity
Because the rate of erosion increases very rapidly with an in-
crease of muzzle velocity, as will be illustrated in detail later
(Sec.10$), a muzzle velocity of about 3000 ft/sec is the upper limit
that may be employed at present without decreasing the life of a gun
too much.' Actually, even most high-powered guns are rated at some-
what lower muzzle velocities.
V Dr. P.R. Kosting, of Watertown Arsenal, in commenting on
this statement pointed out (private communication, Aug. 22, 1?42)
that ’’the phenomena accompanying the change in bore diameter at the
muzzle end are different from those at the breech end,11 and in parti-
cular, that ’’metallographic studies reveal that there is a dif-
ference in the effect of service on the bore metal between the muzzle
and breech end. In discussions of erosion one hears frequently of
references to the wear at the muzzle end and the erosion at the breech
end.’1 The distinction that Kosting makes with respect to the
phenomena is probably valid; but until we are certain that this dif-
ference is anything more than that caused by modification of the
same agent by two different sets of local conditions, it seems un-
necessary to introduce an extra term in referring to it. Conversa-
tions with Navy personnel have shown that they still use the term
"muzzle erosion.”
- 3 -
The depth of penetration of amor plate by a projectile in-
creases as a function of the striking velocity of the projectile.
At relatively low velocities — up to about 2£00 ft/sec — the depth
of penetration of a projectile is proportional to approximately the
three-halves power of its striking velocity as is indicated by such
2/
empirical formulas as that of de Marre [1886]-7 which is still in
use today [Naval Ordnance, 1939]- Whether this same relation holds
true at velocities exceeding 2J?00 ft/sec is not known with certainty.
It has been claimed that the phenomenon of penetration is different
at hypervelocities — greater than, say, 3!?00 ft/sec — and that at
such velocities projectiles made of lead or other soft metal will
penetrate armor as well as steel projectiles. This opinion, which
has not been substantiated as yet, was extravagantly insisted upon
by Gerlich [1930, 1931, 19331> and it has been repeated even by
Hayes [1938, p. 670]. Be that as it may, a gun firing at a muzzle
velocity of nearly $000 ft/sec would be an especially effective weapon
against the armor carried by tanks, because in this way it would be
possible to deliver a projectile having a striking velocity of over
3000 ft/sec at battle ranges up to 1000 yd, and also because the
decreased time of flight and flat trajectory would reduce the un-
certainty in the estimation of range and position,
The probability of hitting an airplane is increased by de-
creasing the time of flight of the projectile, which may be accomplished
2/ The name of an author followed by an underscored date refers
to the appended bibliography.
by increase of muzzle velocityThe experience of the present
war led the Director of Artillery of Great Britain, for instance,
to suggest that there is need for an antiaircraft gun capable of
sending a projectile to a height of 10,000 ft in only 3 sec, which
would require a muzzle velocity of between £000 and 6000 ft/sec
[O.B.P., 19М].
""	I
The attainment of such high muzzle velocities is prevented,
not by the impossibility of designing a gun to produce them, but
simply by the realization that such a gun of conventional design
would erode so rapidly that its use would not be economically fea-
sible. Therefore, if a means of greatly retarding erosion could be
discovered, it would not only increase the life of guns in general,
but also it would permit the development of these special weapons
having high muzzle velocities without bringing in the complication
of novelty of design.
h. Outline of the present survey
A discussion of some of the elementary features of the con-
struction and firing of guns has been included in this report, so
that the main discussion may be understood by a reader who has had
no previous acquaintance with ordnance. This is especially necessary
3/ In a recent discussion of this subject, Weaver [19U2] con-
cluded that "in general the probability of hitting varies with at
least the inverse second power of the. time of flight; and with an
inverse power of the time of flight which may be 3, 4, 5 or even
6 in cases progressively complicated by more severe dodging."
Earlier Kent [1933] had calculated that the probability of hitting
a maneuvering airplane varies inversely as the fourth power of the
time of flight.
- 5 -
because this report is primarily intended for the use of civilian
scientists. Although these scientists are technically well quali-
fied to investigate the problem of erosion of guns, ordinarily they
have had no more opportunity to become acquainted with the details
of ordnance than most ordnance officers have had to learn as much
as they would like to know about the pure sciences underlying the
applied science that is a part of ordnance. Those readers who are
familiar with ordnance, therefore, may well omit Chapters II, III
and IV and a few sections in some of the later chapters*
The design of some parts of a gun affects the rate of erosion,
and therefore a description is given in the present volume of certain
features of gun tubes, projectiles, propellants and the conditions of
firing, so that the necessary information will be at hand for later
application in a discussion of the relation of these factors to
erosion. Other parts of a gun — the breech mechanism, the firing
mechanism, the recoil system, the carriage or other mounting, the
aiming and laying devices, and the fire control instruments — do
not affect the progress of erosion and therefore they are not dis-
»
cussed.
In the second volume — Chaps. VIII to XV — erosion is con-
sidered as a result of the interaction of the gun tube with its en-
vironment during the few thousandths of a second that elapse during
firing. The eroded surface is described in detail and then the effect
of varying the different factors of the environment are set forth to
the extent that information concerning them is available. The experi-
mental methods of study of gun erosion are described; formulas for
- 6 -
the life of guns are summarizedj and finally, some of the theories
that have been suggested to explain the erosion of guns are dis-
cussed.
- 7 -
h./
CHAPTER IIA GUNS
%. Classification
Guns are classified first, with respect to purpose, and second,
with respect to size. To a certain extent the two systems are not
mutually exclusive, for the use of the weapon often demands a cer-
tain size in order that it should be effective. The purpose of the
gun is related to erosion only in so far as it may be reflected in
the design or in the conditions of firing — for instance, the
large projectile and low mutzle velocity of a howitzer or the rapid
fire of an antiaircraft gun.
The size of a gun is measured in terms of the diameter and the
length of the bore. The diameter, which is called the caliber of
the gun, is the principal dimension. The length of the gun from
the muzzle to the face of the breech block is usually expressed in
terms of calibers, that is, it is expressed as the ratio of the
actual length to the diameter. Table I shows the dimensions of a
representative series of guns.
Guns may be broadly classified on the basis of caliber into
small arms and cannon (or artillery). A .£o-caliber machine gun
is the largest size, standard small arm, and a 20-mm gun is the
smallest size cannon in the U.S. Army. The old classification of
artillery into guns, howitzers and mortars has lost some of its
h/ Most of the information contained in this chapter, for
which no other source is indicated, has been taken from Hayes
[193.8] or from Naval Ordnance [1939].
Table I. Principal dimensions and other d,ta.lls of representative guns and their proj,ctiles. (Tak,n by parmission from offical drawings in
the Ordnance Department, U. S, Army.1)
Oun*	.30-MG Ml 7A1	.ui-ua М2	20-ram Ю ,M2	37-nn Ю	75-mtajJ М2-М3	3-in. AA М3	90-ram AA M1	105-™ AA М3	h.7-in. AA T2	155-sbb Ml	8-in. Mk VI	U-ln. M1920M2	t6-in. M1919M3
Construction [b]					Monobloc	Built-up	Monobloc	Monobloc	Monobloc	Built-up	Built-up	Built-up	
	Monobloc	Monobloc	Uonobloc	Monobloc	sone CW	CW liner	cw	cw	cw	2 hoops	linsr	liner	Wire-wound
Muzzle velocity(ft/sec) Pressure} desired max. (Ib/in?)	2800	2800	2850	2600	1850-2050	2600	2700	2800	3150	2800	2750	2650	2700
	118,000	he,000	112,000	36,000	36,000	3h,000	38,000	36,000	38,000	36,000	38,000	38,000	38,000
Tube, length (calibers) — diameter at breech:	72	72	85.5	53.5	28.5-37.5	50	50	60	60	h5	h5	50	50
inside (in.)	O.h7	0.80	0.98	1.98	3.21	3.90	h.71	5.81	7.o6	7.1)0	11.00	16.5	22.0
outside (in.) [c]	1.10	1.68	2.05	h.75	6.60	6.12	10.60	15.50	i5.o	ih.6	12.2	19.5	26.2
Bore disaster,lands (in»)	0,300	O.pOO	0.787	1-1*57	2.950	3.000.	3.5b3	h.13b	h.700	6.100	8.000	11). 000	16.000
— groves (in.)	0.308	0.510	0.81?	1.1)97	2.990	3.080	3.623	h.22h	h.79O	6.200	8.11)0	1h.2h0	16.21)0
Depth of rifling (in.)	o.ool)	0.005	0.015	0.020	0.020	o.oho	0.01)0	0.0h5	o.oh5	0.050	0.070	0.120	0,120
Travel of projsettle(inJ	21.75	33.25	63.68	69-95	72.5-99.2	127.73	156.1)	221.3	2h0.l)	238.3	298.9	60h.7	679.5
Length of rifling (in.)	21.25	31.75	63.08	68. h5	69.6-96.2	125.83	152.1)	216.7	2hi.6	230.6	288.8	598.3	667.5
Twist of rifling	1/33.3	1/30	1/25.586	1/25	1/25.59	i/ho	1/32	1/30	1/30	1/25	1/25	1/32	1/30
Number of grooves	ll	8	9	12	21*	28	32	36	h2	h8	61)	136	llih
Width of grooves(in.)													
[d]	0.167	0.13	0.205	0.231	0.21)8	0.187	0.198	0.211	0.202	O.2h9	0.236	0.173	0,209
Width of lands (in.)	0.06	0.06	0.068	0.15	0.139	0.15	0.1S	0.15	0.15	0,15	0.157	o.i5-	o.ih
Boeder chamber,													
length (in.)	2.75	h.25	h.2h	9.20	13.89	2h. 17	2h.25	31.1)7	hO. hO	1)6.80	71.21	102.66	157.3
—* net volume(in*)[•]	0.25	0.98	2.22	19.92	80.59	200	300	600	10h6	1596	5156	19,377	39,960
Charge (lb)	5o gr	250 gr	0.07	0.50	2.00	h.875	6.82	11	2h	30	98.5	h60	832
Density of loading	0.7?	1.01	0.87	0.695	0.686	0.675	0.629	0.508	0.66	0.63	0.52	0.66	0.59
Projectile type [f]	Ball 112	Ball Ml	H E Mkl	АР U51B1	HEHh8[g]	И E Mh2A1	H E U71	И E M38A1	Я E «73	И E M1O1	АРМкХХМЗАРИс VI		АР Mk IX
Fuse	None	None	Mkl/A/	None	Point det. 1Д9	Mh3 A2	Mh3 A2	lih3 A2	«61	Point det. Base det, M51 Mk X		Mk X	Mk X
Projectile,													
— weight (lb)	150 gr	708 gr	0.286	1.92	11). 60	12.81	23.h	32.77	50	9h. 86	261.8	1560	23h0
— length (ln.)[h]	1.12	2.38	3.25	6.36	15.00	10.19	I6.3h	17.96	23-50	27- Sh	38.18	62 [i]	7211)
— body diameter (in.)	0.3095	0.5115	0,770	I.h53	2.928	2.980	3.520	h.10	h.67	6.07	7.95	13.93	15.93
Rotating band, diam.													
(in.) [J]	—	—	0.828	1.507	3.011	3.098	3.6h3	h.2hh	h.82	6.180	8.16	1h.17	16.2h
— width, total (in.)	—	—	0.197	0.7h	0.1)9	1.02	1.20	1.1)2	2.25	2.02	3.30	h.65	5.33
— width,cyl. (in.) [k ] — dist.from bese	—	—	0,170	0.37	0.35	0.87	1.00	1.17	1,65	0.95	2.13	3.66	3.53
(in.) [1]	—	——	o.ho	0.58	2,22	1.20	2.60	3.02	3.53	3.1)5	2.00	not specified	
Bourrelet, diameter(in.) — clearance - lands	——	——	O.?8h	[0]	2.91)5	2.995	3.537	h. 128	h.693	6.092	7.977	13.98h	15.982
(in.) [n]		**	0.003		0.005	0.005	0.006	0.006	0,007	0.008	0.023	0.016	0.018
— width (in.)			—	0.25		1.h80	0.5	0.75	o.85	0.78	1,1	1.62	2.33	2.67
— dist.from base(in,)[m]	—	—	1.92	—	6.27	5.30	7.23	7.98	8.80	7.h8	10.78	not specified	
» See pp.10 ff for notes concerning the purposes for which these guns are designed.
Footnotes for Table I
[a]	The М2 and М3 guns differ in length <нйу> and hence in mussle velocity*
[b]	CW: ’♦cold-worked.'1
The liner of the 3-in. gun is loose. Those of the 155-mm, 8-in. and 1 Ц-in. guns are shrunk in place.
The smaller guns, up to and including the 105-srn, use fixed ammunition; the U.7-in, gun is separate loading with the powder packed in bage
in a cartridge case; and the 155чпт and larger guns use separate-loading ammunition without a cartridge ease.
The machine guns are automatic. The 75-™» 3-in., 9O-m and 105-mn guns are semiautomatic; that is, the force of the explosion ejects the
fired cartridge case and leaves the breech so that it closes automatically when another cartridge is inserted by hand.
[c]	Outside diameter of the tube or liner. Over-all outside diameters of the built-up guns are: 3-in,, 9.00 in.; 155-чвт, 18.8 in.; 8-in.,
33. $ in.; 1h-in., Ц8 in.; 16-in., 65.8 in.
[d]	The width of the cutter fixes the width of the grooves. The width of the lande ie a nominal residual dimension.
[e]	For small arms ammunition this volume is called the '♦powder space," but on drawings of cannon using bag ammunition the ’’powder space” is
the linear dimension from the obturator pad to the base of the projectile. The "volume of powder chamber" of cannon is the net volume
between the obturator pad and the projectile of a bag-loaded gun, and the net volume inside the cartridge case of a c&ee-loaded gun,
allowing for the volume of the primer, wade and base of projectile.
[f]	AP: "armor-piercing"; H E: "high explosive."
The projectile listed for each gun is the standard one now being manufactured, although older models on hand are still issued for service.
Frequently a different projectile may be fired from the earns gun; or the earns projectile may be fired at reduced charge and hence with
lower velocity.
[g]	An AP projectile (M5l) is used with almost equal frequency. It differs from the H E type in the following dimensions: weight, 1Ц.Ц0 lb;
length, 8,91 in.; rotating band, O.?6 in. from base; bourrelet, O.!>1 in. wide and 5.0o in. from base. A semi-armor-piercing projectile
(M7U) that is also frequently fired differs from the AP type in not having a cap and windshield.
[h]	Length includes fuze, if any, and windshields on AP projectiles.
[i]	This dimension is not specified. The one given is an approximate one taken from a scale drawing.
[j]	The rotating bands on the larger projectiles have a "hump" that projects beyond the main cylindrical portion. The diameters of these "humps"
for the several projectiles are: b.7-in., Ц.98 in.; 155-ran, 6.320 Ln.; 8-in., 8.36 1л.; 1 Ц-in., 1Ц.Ц0 in.; 16-in., 16.58 in. The top of
ths hump is only 0.0$ to 0.1 in. wide.
[k]	All rotating bands are beveled at the front end, and those on ths larger projectiles also at the rear. The cylindrical portion is cut by
from one to five circumferential grooves known as cannelures, which provide space for the copper to flow into during the engraving.
[1]	The distance to the rear of the rotating band or bourrelet.
[m]	This projectile, which Is of the so-called shot type, has no bourrelet. Ths clearance between the body and the lands is only О.ООЦ in. on
the diameter.
(nJ This clearance is the minimum. The tolerance on the diameter of the lands is *0.002 in. and that on the diameter of the bourrelet is
-0.005 in., so that the tolerance on the clearance is *0.007 in.
- ю -
Notes on the purposes of the Guns Listed in Table I
The ,30-caliber M1917A1 Browning machine gun is the standard
ground machine gun, and is also used as an auxiliary antiaircraft
weapon. It is a.recoil-operated and belt-fed automatic gun fir-
ing at the rate of hOO to $2$ shots/min from a tripod mount. It
is water-cooled.
The .50-caliber М2 Browning machine gun is made up in three
types — water-cooled, heavy barrel-(air-cooled) and aircraft
(air-cooled) — by assembly of the proper barrel and jacket on a
basic receiver. The water-cooled gun is the principal antiair-
craft machine gun of antiaircraft regiments. It fires at the rate
of. 600 rounds/min from a tripod mount.
The 20-mm. guns Щ and М2 are automatic aircraft weapons
mounted either for firing through the hub of the propeller or as
a fixed gun in the wing. The rate of fire is 600-700 rounds/min.
The only difference between the M1 and М2 guns, tins former of
which is a substitute standard, is in the dimensions and shapes
of some' of the receiver parts.
The 37"ПДП gun М3 is the smallest field gun used by the in-
fantry and cavalry in the U, S. Army, It is intended especially
for antitank service. Its carriage Mh, which is designed for
great mobility over any kind of ground, can be controlled by one
man. The gun is manually operated, Its tube can be easily un-
screwed from the breech ring for replacement when it becomes over-
heated or worn out. This gun fires both armor-piercing (1,92-lb)
and high-explosive (1.63-lb) projectiles. The 37~mm gun M1A2,
which is the standard antiaircraft weapon of this caliber, is an
automatic gun firing a lighter projectile (1.3h lb) than gun
at a rate of 120 rounds/min, with a muzzle velocity of 2600 ft/sec.
This gun is slightly longer, and the twist of rifling is 1/30.
The 7^-mm guns №2 and М3, which are the same except for
length, have been designed for mounting on tanks. The former is
a’substitute standard, to be used as long as the stock on hand
lasts. They are recent (19h1) adaptations of the original 75-mm
gun M1897 (French), Ballistically, the пот guns differ .from the
M1897 only in length. They use the same ammunition, The longer
of these guns is nearly 20 percent lighter than the Ы1897А2 gun
because it is of monobloc construction.
The 7^-mm gun M1897A2? which is still the standard light
field gun, is Ju,5 calibers long and has a muzzle velocity of
1950 ft/sec. The 7^-mra guns, Ml916 (LT. S.) and И1917 (British),
which are limited standards'.for this same service, are only 28.h
calibers long and have a muzzle velocity of 1900 ft/sec. Their
most distinctive feature is that they.employ rifling of increas-
ing twist. These light field guns are to be superseded by the
103-mm howitzer М2Д1,
- 11
The 3-in, ДА gun,М3 is now a limited standard, to be super-
seded eventually by the 90-mm gun M1of which production was
started in 19U0. The loose liners for the 3-in. gun continue to
be made. These two guns are mobile antiaircraft weapons. Al-
though the 90-mm gun has about ope-third greater maximum range
and fires a much heavier projectile at approximately the same
rate of fire (2$ rounds/nin), the total weight of the gun and
mount is less than 20 percent greater than that of the 3-in.,gun,
because improvements in metallurgy, especially in cold-working,
have made possible monobloc construction.
The 10^-mm AA gun М3 is now (19^2) the standard fixed heavy
antiaircraft weapon? The li,7-in, AA gun T2 is an experimental
heavy mobile model under development. Just as the substitution
of the 90-mra for the 3-in. gun gives increased effectiveness in
light antiaircraft guns, so the h..7-in« is designed for use against
targets at higher altitudes (^0,000 ft) than can be reached with
the 10^-mn gun. This greater range is obtained by the use of
greater muzzle velocity and a heavier projectile of radically im-
proved ballistic form.
The 1^-mm gun Ml Al is the most powerful of the standard
heavy mobile artillery weapons. (The others are the l5£-mm,
8-in. and 2h.0-mm howitzers, all of which have lower velocities
and shorter ranges.) It differs from the 1^5-mm gun M1 only in
the breech ring, but it differs from the old 155-mm gun Ml916
G. P. F. ("Grand Puissance Filloux"), which it superseded in
19^1, by having greater power. The M1916 gun, which was only 32
calibers long, fired a high-explosive projectile of the same
weight at a muzzle velocity of only 2Ц10 ft/sec, using a charge
of 26 lb.
The 8-in, gun Mk, VI, M3A2 and the 1h-in. gun М192ОЫЗ are 
the principal standard railway artillery. The former gun has
been constructed by rechambering one designed by the U, S. Navy.
The 16-in. gun Iu1919M3 is a limited standard for the primary
armament of harbor defense installations. It is not expected, how-
ever, that any more wire-wound guns will be produced. The
present standard for new installations is the 16-in. gun Mk. IIM1,
which is a built-up gun obtained from the Navy,
- 12 -
precision; but these' names still denote differences of length that
are implicit in the different purposes of the three types. A gun,
in this special sense of the word, is the longest, heaviest type
of weapon of a given caliber and has the highest velocity and the
longest range. A howitzer is shorter and lighter and has a lower
velocity and a shorter range. A mortar is a very short weapon that
*
is fired at a high angle of elevation with a relatively short range
for indirect fire. Th® term gun is also used in a special sense to
refer to the tube (or tubes and jackets in a built-up gun) and
breech mechanism as a complete unit as distinguished from the mount,
which includes the recoil mechanism.
6.	The tube
A gun must have walls strong enough to withstand the internal
pressure of the powder gases. Because this pressure diminishes
toward the muzzle, the wall thickness of the tube can be tapered in
that direction. Right at the muzzle, however, the wall thickness
of a large gun is usually increased somewhat to form the so-called
*
bell muzzle, in order to make up for the loss of strength occasioned
by the ending of the tube. The necessary strength of tube throughout
its length is obtained by using a proper thickness of high-grade alloy
steol having a high tensile strength. In addition, large guns are
made stronger -- or rather, equally strong with thinner walls — by
putting the inner layers of the tube under compression. This is
accomplished by wrapping the tube with several layers of wire under
tension, by shrinking on the tube a jacket and one or more steel
hoops, or by expanding the bore beyond the elastic limit of the steel
- 13 -
by hydraulic pressure before it has been machined to final dimen-
sions. Wire-wound guns, although still in service, are no longer
constructed in this country. Built-up guns are frequently made
with two slightly tapered coaxial tubes, the inner one of which
constitutes a liner that can be replaced after it has worn out.
The replacement requires that the tube be sent to an arsenal, for
it has to be expanded by heating in order to disengage the liner,
which is made with a taper of about 0.003 times the diameter per
inch. The use of a loose liner that can be screwed into a small-
caliber tube by the gun crew was tried by the U.S. Army in its
3-in. antiaircraft gun, but it was discontinued because of the
difficulty of replacement under field conditions. The British Army
has used a loose liner with some success in their 3*7- and h..5-in.
antiaircraft guns.
d/
The process of radial expansion^ — called also autofrettage
and cold-working — has been applied to guns up to 8 in. in diameter.
A hydraulic pressure of 110,000 to 1^0,000 Ib/in? is used to produce
a permanent enlargement of the diameter of the bore amounting to
about 6 percent; then, after the pressure is removed, the outer
layers contract and place the inner layers of the tube in a state
111 11 11 ""  ' ...... .................. 1 111 ......................
5/ This process, which was originated by the French "auto-
frettage” is French for "self-hooping"), has been developed by the
Navy at the Naval Gun Factory, Washington Navy Yard, and by the Army
at Watertown Arsenal. A number of reports from Watertown Arsenal
dealing with the development of the process are on file in the
Ordnance Library, cataloged under "Cold-working.” In 19M, equip-
ment for cold-working on a production basis was put in operation at
Watervliet Arsenal.
- Ill -
of permanent compression. A radially expanded monobloc tube instead
of a tube -with a replaceable liner is now preferred by the Army for
•small guns, because the former weighs less and hence can be used on
a lighter mount. Also it has been found-that the cost of an entire
monobloc tube is not much moire than that of a liner alone, and much
less than that of a liner and tube (Ord. Dept., 19йОа; II, p. 67].
7.	Tapered bore
Although the bore of an ordinary gun is cylindrical, some guns
having a tapered bore have been developed in order to obtain a higher
muzzle velocity without a corresponding increase of erosion. They
have been reviewed separately [Burlew, 1?li2] .
8.	The rifling
An elongated projectile requires a high rate of rotation for
stability in flight and for the operation of fuzes of certain
types. This rotation is obtained by the rifling cutting into a
layer of soft metal on the circumference of the projectile as the
latter is propelled down the tube. The rifling consists of a series
of helical grooves in the surface of the bore, the depth of which is
of the order of magnitude of 1 percent of the diameter. The raised
portions of the bore between the grooves are called lands. The
twist of the rifling, which is expressed as the number of calibers
of length in one' turn, in combination with the muzzle velocity of
the projectile, determines the rotational velocity of the projectile.
The design of the rifling, in terms of the number, width, depth
and form of the lands and grooves and the degree and uniformity of
- 15 -
the twist, is a complex subject. Although many designs of rifling
have been tried, there is not complete agreement today as to the
most suitable one. The currently produced guns of the U.S. Агщу
have rifling of uniform twist that varies from 1 turn in 25 calibers
to 1 turn in Ц0 calibers. The number of grooves increases with the
caliber, so that the widths, of lands and grooves are approximately
the same for guns of all sizes. The lands are about 0.15 in. wide
and the grooves slightly wider; and the width of each is uniform
throughout the length of a given gun (see Table I).
9.	Effect of design of rifling on erosion
The effect of the rifling on erosion is not very we11.under-
stood, The presence of stress concentrations at the sharp corners
where the lands and grooves join has been mentioned as an important
contributory factor by various writers [Howe, 1918; Justrow, 1923]t
but a quantitative evaluation does not seem to have been attempted.
The strength of the lands in shear was calculated by Justrow [1923],
who considered that the reduction of bearing surface as erosion
proceeds tends to increase subsequent erosion.
The twist of rifling may affect erosion resistance. An erosion
test was made at Aberdeen Proving Ground [Lane, 1933] of a 3-in.
antiaircraft gun liner rifled with straight grooves for the first
23i- in. from the origin of rifling (see Sec. 11) and then with a
twist that gradually increased to 1 turn in Ц0 calibers during the
next 113г in. For the last 7 in. to. the muzzle the twist was uniform —
1 in Ц0. This liner was fired 2950 rounds, for comparison with
another having a uniform twist of 1 in Ц0 over its whole length.
- 16 -
Both liners had been made of carbon steel of the same chemical com-
position and practically the same heat treatment. Both had been
radially expanded, the one with increasing twist slightly more than
the other.
The gun with increasing twist of rifling eroded less than the
other, except at the muzzle, throughout the course of the comparison.
After 29$O rounds, for instance, at the origin of rifling, the in-
crease of diameter of the lands was only 0.182 in. compared with
0.232 in., and of the grooves 0.112 in. compared with 0.166 in.
At the same time, at 10 in. from the- origin, the corresponding in-
creases were 0.088 and 0.113 in. on the lands and 0.0Ц6, and 0,059 in.
on the grooves. The decrease of muzzle velocity after 2000 rounds
was only $0 ft/sec for the liner with increasing twist, but it was
1U£ ft/sec for the other one. The deviations in range were the same.
10. The forcing cone^
The rifling is terminated at the end of the bore toward the
breech by a tapered section along which the diameter across the lands
increases. This so-called forcing cone (called also band slope and
compression slope) continues toward the breech a short distance
behind the point at which the diameter of the lands equals that of
the grooves. Its rear portion forms the seat for the rotating band
on the projectile (see Sec, 18), which is machined to a matching cone;
and the forward portion, along which the tops of the lands are
6/ For a drawing showing the various parts of a gun tube, see
Naval Ordnance (1939), plate 1, Chap IV.
- 17 -
tapered, facilitates the engraving of the rotating band when the
projectile begins to move. The forcing cone is usually about in.
long. At the rear of it; in a gun firing fixed armunition (see
Sec. 21) is the centering cylinder, into which the neck of the
cartridge case fits. The diameter of this cylinder is 0.2 to 0.3
in. greater than the diameter across the lands. Behind it an-
other enlargement of the diameter, called the chamber slope, joins
the centering cylinder with the chamber proper. In guns firing
separate-loading ammunition (Sec. 21), the forcing cone is fre-
quently elongated, and sometimes — for example, in the 1^5-mm
gun M1 — it is combined with the chamber slope, which eliminates
the centering cylinder.
11. Origin of rifling
The origin of rifling is the point along the axis of the
bore that corresponds to the place on the forcing cone where the
lands and grooves have the same diameter; the length of rifling
is measured from this point to the muzzle. In U. S. Amy reports
on the extent of erosion, however, "origin of rifling" refers to
the forward end of the forcing cone, where the grooves have
attained their full depth. In U, S, Navy and also in British
reports, the erosion is commonly measured 1 in. in front of the
true origin of rifling.
12 • The chamber
The chamber is properly that portion of the gun between the
centering cylinder and the face of the breech block; frequently,
- 18 -
however, the term is used to embrace the whole space up to the
2/
origin of rifling, in which case the total length of the tube is
the sum of the length of the rifling and the length of the chamber.
? The ratio of the' diameter of the chamber to that of the bore, which
|. is called the chambrage, varies from 1.0$ in some German guns to
1.50 in the new U.?-in. AA gun M1 of the U. S, Amy. Gun designers
of the U. S, Navy consider 1.20 a desirable ratio [Naval Ordnance,
1939, Р» 86]. The walls of the chamber in a gun using a cartridge
case are tapered, the diameter at the breech end being a few
hundredths of an inch greater than at the forward end, in order
to facilitate removal of the case. In large guns using bag ammuni-
tion, the rear of the chamber is necked down along a conical see--
tion, called the,chamber rear slope, in order to decrease the size
of the breech block.
13. Effect of chamber design on erosion
The greater the chambrage, the greater is supposed to be the
 erosion. According to Hugoniot and Sebert [1882] , Charbonnier
[1908, 1922] and Tulloch [1921], a bottle-necked chamber causes
eddying of the powder gases at the origin of rifling, with the
result that local washing action on the wall is set up. The
effect of such turbulence was demonstrated by de Bruin and
de Pauw [1931] in the case of an erosion vent plug (see Sec. 86)
by means of a plug made in three parts. The first and third
parts had holes 1 ип in diameter and 10 nn long, whereas the
7/ The term is used in this way in Table I.
- 19 -
intermediate section had a hole 7 mn in diameter and 5 mm long.
When such a vent plug was fired, using йО-percent NG powder, at
a maximum pressure of 1Я00 atmos, the third part of the plug
eroded more than the first, even though the. gas had lost sone of
its energy.
The recommendation made by Hugoniot, Charbonnier and Tulloch
that the chamber should not be much greater in diameter than the
bore seems plausible, but no quantitative data to support it are
known to exist. The reason for this is that ordinarily when two
guns of the sane caliber are made ’with chambers of different dia-
meters, all other features of the design are not kept constant.
The chamber of larger diameter, for instance, will have a larger
volume and hence the correspondingly larger charge used in it
nay be the sols cause of the increased erosion (see Sec, 10!?).
14. Examination of the bore
The surface of the bore of a gun is examined by moans of a
boresearcher, which consists of an illuminated mirror and a tele-
scope, For bores of diameter 6 in. or less, the two parts are
combined in one. instrument, called a boroscope, which may be
quickly focused on any part of the bore surfacef For measure-
ment of the diameter of the bore, an instrument called a star
gage is used. It consists of either two or three measuring points
that nay be extended radially in a plane by the movement of the
handle at the opposite end of a long staff until the points make
contact with the wall of the bore. Thon the diameter nay be read
from a scale — either vernier or micrometer — on the handle.
- 20 -
All guns are examined with a boresearcher and measured with a
star gage at the time of manufacture,
8/
1$. Steels used for gun tubes and liners
The U. S« Navy has used for many years a plain carbon steel
for its gun liners and a 3-perccnt nickel steel for tubes, hoops
and jackets. Typical compositions of these two steels are given
in Table II, The nickel steel differs from the carbon steel only
in its nickel content and in having a slightly smaller amount of
carbon. Tho yield strength of the gun stoc-1 must be at least
$3,000 Ib/in? and that of the nickel steel at least 6$,000 lb/in?
(Naval Ordnance, 1936].
Table II. Chemical composition, in percentages, of steels
used in U. S. Navy gunsT
	0	Mh	Si	P	s	Ni	SAfe No.
Gun steel	0.42-0.50	0.70	0.27	0.03	0.03	0	io4o
Nickel steel	0.35-0,42	0.70	0.27	0.03	0.03	3.00	2340
*After Naval Ordnance [1939]. pp. 118-119.
The U. S. /.rmy uses a variety of different compositions of
low-alloy steels for gun tubes end liners, procured on the basis
of a macro-etch test and tensile properties. Ths following quota-
tion from Notes on the selection and use of motels in ordnance
design [Ord. Dept., 1940b, p. 86], prepared at Watertown Arsenal,
explains tho presont policy.
8/ Tho relation between ths properties of the gun metal
and erosion is discussed in Chap. XI.
- 21
"dhemical compositions are normally not prescribed because
other factors Such as proper melting and finishing of the metal
and its final cleanliness play an important part. The method of
pouring, size, relative dimensions and shape of molds, proper
method of reduction in hot working, and heat treatment in various
stages of the process are also important in securing the quality
of product desired in gun steels.
'Every manufacturer, depending on his equipment, staff, con-
ditions of work, etc., as well as his previous experience and
traditions, will have a preference for certain definite composi-
tions. It is advisable to let the manufacturer choose his own
composition and assume the responsibility for his work so long as
the physical and metallographic properties are satisfactory for
gun material.
"In normal gun steels, the designer is primarily interested
in the physical characteristics obtainable. Specification 57-103
provides for the following physical properties:
Yield strength
Tensile strength
Elongation
Reduction of area
65,000 lb/in!
95,000 Ib/in?
18.0 percent
30.0 percent
The trend, however, is toward the following requirements which
have been found more practical for Ordnance purposes:
For tubes and liners (medium strength) —
Yield strength (set, 0.05 percent) 65-60,000 lb/in?
Reduction of area	h5.0 percent minimum
For 37-mm, 1.1-in., etc. (high strength) —
Yield strength (set, 0.05 percent) 95-110,000 lb/in^
Reduction of area	lj.5.0 percent minimum
The above values are readily obtainable in centrifugal castings,
and the manufacturer of forgings can meet such requirements with
reasonably clean steel.
"The procurement of gun tubes and liners produced by the
centrifugal casting precess is covered by specification 57-66.
The high ductility from transverse specimens in the cose of
centrifugal castings is due to the method of manufacture, which
definitely eliminates the directional properties always present
in forgings,"
The compositions of a number of forgings end centrifugal
castings used in guns recently completed by the irray are listed
in Table III. The tonsile properties of these steels exceeded
- 22 -
Table III. Chemical composition, in percentages, of
steels currently used in Lrray' guns#
Element	A	в	c	D
C	0.20-0.211	0.31-Q,3H	0.3I1-0.35	0.1x3-0.1111
Mn	0.60-0.90	0.61-0,77	0.71-0.73	0.59-0.67
Si	0.15-0.23	0.20r0.3Q	0.2	0.18-0.26
P	0.006-0.011	0.027-0,035	0.01Ц-0.0211	0.012-0.02
S	0.016-0.018	0.029-0.038	O.O19-O.O23	o.oi5-o.oi8
Mo	0.Ы1-0.53	0.32^0,38	0.30-0.35	0. li 7-0 .h9
V	0.06-0.16	Q,1?*-0r?3	0.00-0.06	0.19-0.21
Cr	0.91-1.08		0.53-0.97	О.19-О.ЗО
Ni	——	—	2.26-2.116	0.18-0.36
‘’'Frcrn Record of measurements -and report of inspection, in
the files of the ..rtillery Division, Ordnance Department, U. S.
Amy.
A.	Range of compositions of 111 centrifugal castings made
in 19110-Ii1 for 37-mm and 90-mri gun tubes and 3-in. Ал gun liners
to be either heat treated to strength or cold-worked.
B.	Range cf compositions of 8 forgings made in 19110-111 for
155-mm gun tubes, to be cold-worked.
C.	Range of compositions of 3 forgings made in 19110-Ц1 for
75-nm gun tubes, to be heat treated to strength.
D.	Range of compositions of 3 forgings made in 19UO-111 for
6-in. gun liners, to be heat treated to strength.
the requirements just quoted. The composition of the centrifugal
castings in column A represents a development at Waterterm ..rsenal,
Donald {19371 recommended essentially this same composition ex-
cept for carbon content (0,35-0.110 percent) for making a centri-
fugal casting to be heat treated to a yield strength of 125,000
lb/in?, ns a result of a tost of 32 experimental castings of
various compositions. Bender and Pappas [19111j, after a study
of five slightly different compositions, confirmed the choice.
- 23 -
Their work showed that the variations in chromium and manganese
had only minor effects on physical properties, but "that sub-
stantial changes in physical properties may be brought about by
changes in carbon content," The higher the carbon content, the
higher the yield strength. Bender and Pappas recommended 0.30-0,35
percent carbon for a yield strength of 121,000 to 125,000 Ib/inf
For rifles and machine guns the formerly used manganese
steel, W. D, (S.h.E.) 1350, has been superseded by a chromo molyb-
denum steal, W. В. (S.h.E.) 4140 modified, which han been found
to increase the service life. The compositions of these two
steels are given in Table TV. For bans up to 2 in. in diameter
the minimum yield strength specified is 110,000 lb/in®, the
minimum elongation is 18 percent and the minimum reduction of
2/
area is 50 percent. Those tensile properties represent a consider-
able improvement over those of the 23 alloy steels that had been
tested (see Sec, 92) in the form of machine-gun barrels at
Springfield ..mory in the early nineteen-twenties, only one of
which had contained any molybdenum.
Table IV,' Chemical composition, in percentages, of
stools used in small arms barrels.
Element	W.D. 1350	W.D, 50 Nod.
C	0.45-0.55	0.45-0.55
bin	0.60-0.90	0.60-0.90
Si	— ——	O.15 max.
P	o.o45	0.025 max.
S	o.o55	0.025 max.
Or	—	0.80-1.10
No	•—••	0.15-0.25
9/ U.S. .xrmy Specification No. 57-107-25, Oct., 11, 1939.
- 2k -
16.	Yield strength
The yield strength referred to in the foregoing section is
determined by the ’’offset method” as described in ’’Federal speci-
10/
fications for metals,” In this method the extensometer reading
is plotted as a function of load — by on autographic extenso-
meter in many cases — until the curve is no longer linear. Then
a straight line is drawn parallel to the initial straight portion
of the extensometer curve and offset from that curve by an amount
equal to a prescribed set — for example, 0.0^ or 0.1 percent of
the gage length. The load corresponding to the point of inter-
section of this line and the extensometer curve, divided by the
original cross-sectional area of the specimen, is the yield
strength. The value of the set now prescribed — usually 0.0f>
percent — was chosen so that the resulting yield strength
corresponds closely tc that determined by the proportional
method, which formerly was used for inspection.
For a given sample, the yiold strength is numerically
Ц/
larger than the proportional limit, the elastic limit or the
12/
proof stress. As defined in the same specification, these three
10/ Federal Specification [ч^-М-151а, Nov, 27, 1936, par.
22g(2jj; published in the Federal standard stock catalog, Sec.
IV (part 5),
11/ The yield-strength determined by the proportional method,
which should not be confused with the proportional limit, is de-
fined in Federal Specification QQ-M-15>1, par. 22g(l) as follows:
11 Proportional method. — The yield strength shall be calculated at
the reading last preceding the first increment of load which pro-
duces an increment of strain which clearly exceeds twice the
increment of strain taken from the modulus line.”
12/ Footnote 11, pars. 37a, b and c.'
- 25 -
limiting stresses correspond, respectively, to 0, 0.003 and 0.01
percent permanent elongation. The yield point, on the other hand,
J3/
corresponds to an extension under load of 0.5 percent or greater;
and the tensile strength is the greatest load per square inch of
original cross-sectional area carried by the material during a
tension test.
13/ Footnote 11, pars. 22h and 37o
- 26 -
CHAPTER III. PROJECTILES
17.	General description of projectiles
Modern projectiles are' elongated to secure a largo ratio of
mass to cross-sectional area, and.thereby long range. The head
of the projectile is provided with a curved surface in order to
/
decrease the wind resistance 5 and, similarly, the rear end is
frequently tapered slightly to give a boat-tailed shape, which
reduces air resistance at velocities in the region of the
velocity of sound. The longitudinal cross suction of the head
is bounded by an ogive, which is an arch-shaped curve, the two
branches of which are arcs of two large circles of the sane
radius intersecting at the nose of the projectile. The longi-
tudinal axis of the projectile' is the perpendicular bisector of
the line joining the centers of these two circles. The radius
of the ogive, ’which is the radius of the two circular arcs, is
expressed in-calibers. Small urns projectiles, which arc called
bullets t have a soft outside jacket of copper alloy of diameter
large enough to be cut by the grooves of the rifling. the
rear of a bullet is a circumferential groove, called a cannelure,
into which the mouth of the cartridge case is crimpud,
Лп artillery projectile is so long that, in order to keep
it centered in the bore, it is provided with a bourrelet at the
rear of the head. This is a cylindrical surface that has boon
machined to have a slight clearance in the bore (see Table I).
Behind the bourrelet, which is about ono-sixth caliber wide, the
remainder of the body has a diameter slightly less then that of
- 27 -
the bourrelet, ec that it doos not touch the lends. Near the
rear of the projectile a rotating band (Sec, 18) is shrunk and
forced into an undercut groove machined in the body of the pro-
jectile. The dimensions of the cavity of the projectile and
the location of the center of gravity are features of design
that are important in general but which do not relate to erosion.
The general proportions of artillery projectiles are ex-
pressed in approximate terras in Table V.
Table V. approximate proportions, in calibers, of
artillery projectiles#
Length	Ц to 6
Length of head	2-1/3 to 3
Radius cf ogive	7 to 9
Width of bourrelet	1/6
Width of rotating bond	1/3
Length of cylindrical	
part of base	1Д
^nglo of boat-tail	9е to 9е
Weight (lb)	(caliber in inches)3
*.fter Hayes [1938], p. £60.
18.	Rotating band
The rotating bond — called the driving band by the British —
performs taro functions in addition to furnishing a convenient sur-
face for the rifling to engage and thus to spin the projectile.
It centers the rear of the projectile and it seals the forward end
of the powder chamber. Erosion of the gun adversely affects the
- 28 -
performance of all "three of these functions of the rotating band.
The lack of centering of the rear of the projectile in the bore
of a worn gun has been suggested [Miller,. 1920] as a major cause
of the increase of dispersion. The increased opportunity for
leakage of gas past the rotating band (see Chap. XIII) in a worn
case gun (defined in Sec. 21) may account for the increased rate
of erosion generally ascribed to such guns as compared to bag
guns (Sec. 21), in which tho projectile is rammed hone regardless
of how much the forcing cone has been advanced (see Sec. 63).
The band must be both soft and strong to serve its several
purposes. Copper, which was formerly used exclusively, is still
the standard material for the rotating bands of most projectiles
used in Navy guns and of those of larger calibers of seacoast
artillery. Gilding metal — 90 percent Cu, 10 percent Zn — is
widely used for rotating bends by the urmy in order to reduce
coppering (see Sec. 60); but although it was triad by the Navy,
it is now used by that service only for projectiles for the
1Ц/
1,1-in. and 6-in. guns.
The diameter of the rotating band, as may be seen from
Table I, is about 0.02 in. greater than that of the grooves in
a new gun, so that the grooves are completely filled when the
rotating bund is engraved as the projectile moves down the boro.
The starting pressure — or shot start pressure, in British usage —
which is required to engrave ths rotating band, is considered as
part of the friction of the projectile in tho bore (Sec. ЦЦ). A
s1
ill/ Dr. L. T. Е» Thompson, Naval Proving Ground, personal
communication, Sept. 13, 19hl.
-29 -
recant British investigation. [л, C. 19h-2c] has shown that engrav-
ing of the rotating band of a 3-in. proof shot occurred partly by
plastic flow ord partly by shear. The amount of shear increasod
’with the age of the gun after it had been two-fifths worn. It
also increased with the degree of filling of the grooves and with
the hardness of the copper.
Many experiments have been fnade with rotating bands for the
purpose of reducing "fringing.11 Depending upon the design of the
band, excess copper may be dragged back during engraving by the
rifling to form n fringe at the rear edge of the band, and then,
as the projectile leaves the muzzle, this fringe is flared out
by the powder gases and by centrifugal force into a shape like
a hoop skirt, which seriously affects the flight of the projec-
tile . A resume of the modifications of rotating bands tried dur-
ing World VTar I to overcome fringing was given by Veblen and
Alger [1919]• Fringing is eliminated by providing some place for
the displaced copper to flow into, as, for instance, by cutting
a cannelure at the roar of the band.
19.	Effects of the rotating band on erosion
The rotating band may affect erosion in three different
ways. The frictional wear between it and the surface of the
bore (Sec. hh) is generally considered important, although there
is no means of evaluating its contribution to the total erosion.
Some investigators — for instance, Justrow [192-3] — consider
that the frictional wear per se is insignificant, whereas
others for instance, Kosting [1939b] — conceive of it simply
- 30 -
as ths means of ramoval of portions of the bore surface that had
already been loosened by previous chemical or physical action.
Tulloch [1921] suggested that the frictional wear is increased
at tho muzzle by the abrasive action of particles of steel carried
forward from the rear of the bore. At any rate, some evidence
that wide rotating bands caused more erosion than narrow bands
was obtained [Lane, 1933] in the firing of 3-in. antiaircraft
liners (see Sec. 9). In the second place, the design of the rotat-
ing band helps to determine the extent to which gas can leak past
the projectile, which is an effect that is considered in detail
in Chap. XIII. In the third place, the material of which the rotat-
ing band is made may add another factor to these two mechanical
ones by reason of metal fouling, which is considered briefly in
Sec. 68.
20,	Cartridge case
Ammunition is of two general types, depending on whether the
powder and primer are, or are not, contained in a cartridge case.
The cartridge case, which is usually made of drawn brass, also
serves as an obturator to prevent the escape of powder gases
through the breech mechanism. The thin body of tho case at the
forward end is expanded by the gas pressure until it makes a gas-
tight seal with tho wall of the chamber. (Obturation of the
breech of a gun that doos not use a cartridge case is obtained
by means of an asbestos mushroom pad or other gas check device
which is part of the breech mechanism.) The case and the cham- .
her into 'which it fits are tapered slightly, in order to facili-
tate removal of the empty case after firing. The primer is held
- 31-
in a recess in the bottom of the case, so that it is struck by
the firing pin that operates through the breech mechanism. A
cartridge case is only slightly affected by firing, and there-
fore can be used a number of times, if it is resized to the
proper dimensions.
21.	Fixed and separate-loading ammunition
A complete round of fixed ammunition consists of the pro-
jectile and fuze (if any) firmly crimped in the end of a cartridge
case that contains the powder and primer. Such ammunition is used
for small arms and for most guns up to and including the 105-mm
gun in the i.rmy and the 5-in. 25-caliber AA gun in the Navy. It
is essential for all automatic and semiautomatic guns.
Semifixed ammunition, in the nomenclature of the U. S. Army,
differs from fixed ammunition only in that the projectile is
loose in the end of the cartridge case and the powder is in bags.
This type of ammunition is employed for guns, such as the 105-mm
howitzer, that use charges of different sizes in order to vary
the range. The cartridge case is loaded originally for the maxi-
mum range, and then, if a shorter range is desired, ope or more
bags of powder arc removed. The projectile and cartridge case
are loaded into the gun as one unit. In the U. S. Navy the term
semifixed ammunition has a slightly different connotation. It
is a-form of separate-loading ammunition in which the powdor
charge is packed in a cartridge case for convenience in handl-
ing, but in which the projectile and the cartridge case are
loaded separately into the gun. This manner of loading gives
- 32 -
opportunity to rani hone the projectile against the forcing cone.
The 5-in. 38-caliber AA gun and the latest 6-in. guns of the Navy
use this form of semifixed ammunition. It is also used.in the
nevr Army b.?-in. gun M1 without being designated by any special
name.
Bag ammunitiont which is the general form of separate-
loading ammunition, consists of a projectile, one or more bags
of powder and a primer., Tho powder bags are made of silk cloth,
and an ignition charge is contained in tho base of each. The
primer is attached to the end of the mushroom stem. Bag ammuni-
tion is used for all large guns, which sometimes are called bag
guns as distinguished from case guns.
- 33 -
CHAPTER IV. PROPELLANTS
22.	Classification of explosives
Propellent powders are always low, or progressive, explosives,
characterized by propagation of the explosion — really a very
rapid burning — only on exposed surfaces, by the heating of succes
sive layers to the ignition temperature (see Chap. V). In high
explosives, on the contrary, a detonating wave is transmitted prac-
tically instantaneously throughout the mass after initiation of the
l£/
explosion by heat or shock. Both nitroglycerin and trinitrotol-
uene (TNT) are high explosives, but when either is incorporated in-
to a colloid with nitrocellulose, as is done in the manufacture of
some propellent powders (see Table VI), it loses its tendency to
detonate and merely increases the rate of burning of the mixture.
A Iovj- explosive, on the other hand, may acquire the power to det-
onate under' special circumstances, such as extreme shock.
2.3. Granulation
After General Rodmen of the U. S. Army discovered the
principle of the progressive burning of gunpowder in i860 and
applied this principle by compressing gunpowder into perforated
grains of different sizes, the tern powder as applied to explo-
sives lost its etymological connotation of a pulverized material.
Powders today are produced in the form of cylinders, cords, tubes,
flakes and strips. Most propellent powders in the United States
are made in the form of cylindrical grains, the diameters of
13/ A recent discussion of the theory of detonation has
been given by Carl [1рЦо].
- 311 -
which vary from 0.03 in. for a .30-caliber rifle to 0.9 in. for
a 16-in, gun» . The lengths vary correspondingly from 0..06 to
2.1 in. For a weapon of a given caliber several different sizes
of powder may be used, depending on the type of projectile.
The smaller cylindrical grains have single axial perfora-
tions, and the larger ones have seven perforations parallel to
the axis. Six of these latter perforations aro at the vertices
of a regular hexagon and the seventh is at the center, the dis-
tances. between centers cf all adjacent pairs being nearly’' equal.
Such niultiperforated powders are said to bo progressively granu-
lated, because the burning surface increases as burning proceeds,
and hence the rate of burning increases.
The web thickness, ivhich is the minimum thickness of the
grain between any two boundary surfaces, either internal or ex-
ternal, determines the time required to consume a powder of
given composition. The web thickness of a singly-perforated
grain is g-(D-d) and that of a multipart orated grain is taken as
4(D-3d), where D is the diameter of the grain and d is the
diameter of the perforation [Naval Ordnance, 1939, p. 37].
Hence, the grain diameter is about three times the web thickness
of a singly-perforated grain, and from five to ten times the web
thickness of a multiperfcrated grain,
16/
2Ц. Chemical composition
Gunpowder — frequently called black powder — was used as a
propellant until 188Ц, when Vieilia introduced colloidal smokeless
16/ The effect of the chemical composition of propellants
on erosion is discussed, in Sec. 106,
- 35 -
powder made of nitrocellulose. Today the two general typos of
propellant used by all nations are single-base and double-base
powders. A single-base powder is one in vrhich the principal in-
gredient is nitrocellulose. A double-base powder contains a
considerable quantity of nitroglycerin in addition to nitrocellu-
lose. In both typos tho nitrocellulose is gelatinized by suit-
able solvents. For a single-base powder ether and alcohol are
usually used. The nitroglycerin in double-base powder assists
considerably in the gelatinization, so that if enough nitro-
glycerin is present, no solvent is needed; otherwise acetone is
used. Doublo-basc powders, which give butter ballistic results
than single-base powders, have been standard propellants in
Great Britain and some other countries for many years. . Because
their erosive effect is greater, however, double-base powders
have not been used extensively in the United Status.
25.	American propellents
For many years the standard smokeless propollent powder used
in this country was pyro powder. This is made from "pyrocellu-
lose11 (a nitrocellulose containing 12.6 percent nitrogen) to which
is added 0.5 to 1.0 percent diphonylamino as a stabilizer. This
is still the standard powder in the Navy. J.Iuch of it is still on
hand in the Army, especially for the largor caliber guns; but NH
powder ("nonhygroscopic11) and FNH powder ("flashless and non-
hygroscopic") are tho onos being produced today. The first lot
of FNH powder was made in 192Ц, but the total axiount produced
- зб -
before 1930 was very small, . Therefore> much of the data on the
erosion of guns in the U,. S. services, apply to guns fired with
pyro powder.
The composition of the various smokeless powders, other than
pyro powder, currently used by the U, S, Army are listed in Table
VI, which is based on the confidential specifications of the
Ordnance Department. The NH and FNH powders keep bettor than
pyro powder because they arc less hygroscopic. This property
is obtained by the inclusion of dinitrotoluene (DNT) and dibutyl-
phthalate. Double-base powders in general are less hygroscopic
than singlo-base ones, and hence much less DNT is needed in I.I2-
than in Ш-type powder. These sane two compounds servo also as
coolants in the Mi-type FNH powder, causing the powder gases to
emerge from the muzzle at a temperature below their flash point
when nixed with the oxygen of the air. The flash from FNH, М2
powder is repressed by the inclusion of barium and potassium
nitrates. In some of the snail arms powders it is repressed by
potassium sulfate, and this compound can be used also as an aid
_18/ •
in the Mi-type cannon powder. Flashlessness, which depends, on
granulation and ignition as well as on composition, has been
achieved only to a partial degree in large-caliber weapons. The 
potassium nitrate used in some .of the powders improves tho igni-
tion. The tin and tin oxide were used as docopporing agents
17/ Mr; Bruce E, Andersen, Ammunition Division, Industrial
Service, Ordnance Department, personal communication, ^ug. 29, 19ll1<
18/ FHN/P powder also contains potassium sulfate^ sec last
footnote (*) under Table VIB.
- 37 -
(see Soo. 6?). The graphite glazing on the М2 cannon powder,
which is also used sometimes on other powders of small granula-
tions, is simply 0 lubricant to make the powder flow more readily
and therefore pack bettor.
Attempts have been made from time to time to develop a powder
that would have a high propellent, power without causing a high
temperature in the gun, and that would therefore be flashless and
presumably less erosive. The most successful of such cool powders
12/
arc those based on nitreguanidinc, also called picrite, The
Du Pont Company experimented with nitroguanidine powders for several
years after World War I, but abandoned then after the development
of the present FNH powdor. They 'were found excellent as regards
flashlessness, but were objectionable because of smoke and ammonia
fumes. Also the weight of charge was larger than for pyro powder —
15 percent larger for a 75-mm gun [Storm, 1925>]. Those objections
are considered by the British to be outweighed by the advantages
of flashlossnoss and reduced erosion (Sec, 108); and so they arc
using two picrite powdors (see Table VIB),
26.	British powders
In 1888 a special committee adopted. as standard for the
British services a smokeless powder node by gelatinizing a mixture
of highly nitrated nitrocellulose and nitroglycerin with acetone.
It was called cordite because it was formed in cords of various
*19/ Chemical formula, NH3C(;NH)NHNOg, attempts to make the
dinitro derivative, which would presumably have a higher poten-
tial, have failed. (Dr. G. B. Kistiakowsky, private communica-
tion, ^.pr, 2Ц, 1912.)
- 33 -
Table VI.
Nominal composition in parts by weight of smokeless
powders.
A. American Powders
Ingredient	Cannon Powders			Small Arms Powders					
	NH,M1	FNH,M1	FNH,M2	No.5	DIR 1185	Dffi Ц676	IMR hl 66	IMR h8lh	ECa
Nitrocellulose13	8?.O	85.0	76A5C	99.0	91.0	100.0	97.5	100.0	80. od
Nitroglycerin			19.5						
Dinitrotoluene	10.0	10.0	1.0	1.0	6.5	7.5	10.0	8.5	
Diphenylamine	1.0	1.0	0.60	1.0	0.5	0.70	0.6	0.70	0.75
D ibu tylphthalate	3.0	5.0							
Potassium sulfate						1.0	1.0	1.0	
Barium nitrate			1.Ц						8.0
Potassium nitrate			0.75						8.0
Tin					1.93				
Tin dioxide							1.5		
Graphite glazing			0.30						
aAlso contains 3.0 parts of starch and 0.25 parts of aurine, a red
coloring agent.
^Containing 13.15 percent nitrogen.
Containing 13.25 percent nitrogen.
^Containing 13.20 percent nitrogen.
В. British Powders (Cordites}#
Ingredient	Mk. I	M.D.	к.	W.M.	s.c.	N.	N.Q.
Nitrocellulose®	37	65	65	65	h9.5r	19	21.5’
Nitroglycerin	58	30	29	29.5	hl .5	18.5	20
Picrite						5U.7	5U.7
Mineral jelly	5	5	6	3.5			
Carbamite				2	9	7.5	3.5
Chalk				oA		0.2	0.15
Cryolite						0.3	0.3
Containing 13.1 percent nitrogen,
p
Containing 12.2 percent nitrogen.
*After Littler (19h2). To save space we have omitted from this
table NH, FNH and FNH/p, which are American-made single-base powders
used by the British services. The first two have essentially the
compositions given in Table VIA. The FNH/P contains 1 percent of
potassium sulfate in addition to the ingredients listed for FNH,M1.
- 39 -
Notes for Table VIA
(1) Abbreviations♦ — NH, nonhygroscopic; FNH, flashless and
nonhygroscopic; IMP,, improved military rifle; EC, Explosive Company,
the name of the English manufacturers who first made this powder aft-
er its invention in 1882 [Marshall, 1917> p. h8.J; AP, armor-piercing,
(2) Use of small arms ammunition. —
Caliber ,22, no standard composition.
Caliber .1x5, Du Pont Pistol No, 3,
Caliber .30 (ball and AP), 1925-hO, ЛЖ1185 principally, but
also several lots of pyro and FNH powders; since the summer of
191x1, IMRU676.
Caliber, ,30 (blank), EC,
Caliber ,50 (ball and AP), before 1928, various smokeless
powders to which different metallic compounds had been added;
1928-1x1, EM166; since the spring of 19M, HM8lli.
Caliber ,30 (blank), EC.
Notes for Table VIВ
(1) General notes on British cordites. —
Mark I, the original British cordite (1889)5 still made for
pistol and ’'blank'1 ammunition,
M,D,, manufactured on a large scale for small arms ammunition.
W,, Land Service propellant of improved stability; largely
replaced li,D, after 1932 for major caliber guns.
W ,M,, "Emergency11 Land Service propellant; introduced April
19h0; replaces W,
S.C,, the principal Naval propellant; developed by Research
Department, Woolwich Arsenal and introduced about 1923; made by
solventless process.
N,, mainly used for antiaircraft guns (3,7 and h.5-in.), but
flashless charges have been determined for most guns and howitzers.
N,Q., mainly used for smaller guns (for example, Q.F, 6-pdr)
and howitzers (for example, Q,F, 25-pdr, B.L. 3.5-in., etc,),
(2) Special notes on nomenclature of flashless propellants. —
The shape of the grain (other than cords) or the source of the
nitrocellulose is denoted by the following additions after the
soliduss tube =/T; slotted tube =/S; multitube =/M; nitrocellu-
lose from cotton vraste =/A; nitrocellulose from wood =/F.
The web thickness in thousandths of an inch is denoted by
a figure following the letter; thus, "cordite N/М. 01l8."
- ЦО -
diameters. The original cordite Mk. I caused so much erosion that
the amount of nitroglycerin was greatly reduced to give cordite
M.D. (= "modified"). The mineral jelly (vaseline) in it serves the
double purpose of coolant and preservative [Marhsall, 1917, I:
30h-f>] • The compositions, of these and other more recently devel*«
oped British powders are listed in Table VIB.
Ballistite was invented by Alfred Nobel in 1888 by gelatin-
izing a nitrocellulose of low nitration with nitroglycerin. The
ratio of nitrocellulose to nitroglycerin has varied from h.O/60
to 5o/5O, and various stabilizers have been added. Ballistite
or powders of nearly equivalent composition ’were used by the
German and Italian governments at one time [Marshall, 1917, I:
301-2].
2?. Stability
All smokeless powders deteriorate during storage. Among  -
the.products of decomposition are oxides of nitrogen, which pro-
gressively accelerate further decomposition. Stabilizers act
by combining with these oxides and preventing the acceleration,
without actually stopping the decomposition. The common
20/
stabilizers are diphenylamine, vaseline and "centralite."
Powder that is deteriorating produces objectionable fumes even
before its ballistic properties are impaired. Air-dried pyro
powder has been found to last 30 to Ц0 years, but water-dried
pyro powder lasts ". somewhat shorter time, depending upon the
20/ Also called "carbatnite." The chemical, name is
s-diethyldiphcnyl urea [Pike, 1?h2].
- ы -
siae of granulation and various conditions of manufacture); On
tho basis of accelerated testss NH and FNH powders sere expected
to last considerably longer than even air-dried pyro powder. .
Because both moisture and high temperatures accelerate to some
extent the deterioration of smokeless powder, considerable care
is taken to protect it during storage.
28. Primers
The initial impulse required for the ignition of a charge
of powder is obtained from a small amount of highly sensitive
explosive that can be readily set off by percussion, friction
or heat. Smokeless powder in all but the finest granulations
is so difficult to ignite that in addition to the detonating
element most primers contain an igniter charge of black powder
which burns very rapidljr with a hot flame and ignites the main
powder charge. The best ballistic results might be obtained
if the ignition were simultaneous throughout the charge. This
condition is approached in practice by tho method of distribu-
tion of tho igniter charge, a perforated tube along the axis
of the chamber being frequently used .to contain the black powder.-
Tho proportion of black powder to smokeless powder varies, be-
cause the sane primer is often used with cartridge cases of
several different calibers.
- Ц2 -
CHAPTER V. ' BURNING OF THE POWDER
2?. Effect of pressure on rate of burning
A colloidal propellant burns by parallel layers. This law,
first enunciated by Piobert [1839] in the case of gunpowder, has
been verified for colloidal propellants by the observation that
unburned pieces of powder recovered after having been fired in
a gun retain their original chemical and physical properties be-
low the surface [Crow and Grimshaw, 1931b, p. 392; Muraour and
Aunis, 1938.] Recent observations, however, show that under
certain conditions the burning takes place below the surface as
£1/
well. The rate of burning increases very rapidly with increase
of pressure of the liberated gases. Thus the rate is increased
about a thousand-fold by increase of pressure from 1 to 2^00
atmos
The highest pressure to which smokeless powder can be sub-
jected without having it detonate or burn erratically does not
seem to have been determined. During the test of a certain 37-nim
gun having an extra strong barrel, a series of five rounds were
fired at pressures ranging from 63,hOO to 67,900 lb/in?, as
measured by a piezoelectric gage. The velocities, which varied
from 3355 to 3375 ft/sec, were acceptably uniform. Hence, as
far as the burning of the powder is concerned, a pressure as high
as this might perhaps be used in a hypervelocity gun.
21/ R. E. Gibson, personal communication, July 19^2.
- 43 -
30* The mechanism of the burning process
The surface of a burning solid propellant remains relatively
cold while a gaseous reaction at a very high temperature (Sec. 36)
takes place at a distance of approximately 10'*'’ cm from the surface.
The slow step in the complex process is the transfer of heat to the
surface by the molecules of the burning gas that impinge upon it,
for a surface layer of the solid must be kept at the temperature
of spontaneous decomposition in order that burning may continue.’
Because an increase of pressure means that more hot gas molecules
are available to transfer energy, the rate of burning is increased
by pressure. This view of the burning process has been elaborated
recently by Boys and Corner [1941] and by Lennard-Jones and Corner
[1941]. Crow and Grimshaw [1931b] and Muraour [1931] had suggest-
ed essentially the same theory, except that they had postulated a
cruder method of heat transfer,
22/
Earlier investigators had derived empirical equations of
the form,
. 1. c
r = a + bp ,
where r is. the rate of regression of the burning surface, £ is
the pressure, and a, b and c are empirical constants. Frequently
c was considered unity and a was very small or zero. In such
equations, however, the apparent rate-of-burning constant, b, had
been found to increase und^r conditions giving rise to increased
22/ See Crew and Grimshaw [1931b, pp. 387-8, 397] for
bibliography, Bennott [1921, p. vii], in the'preparation of his
Tablas for interior ballistics, assumed that the rate of burning
of pyro powder is proportional to the two-third powder of the
pressure.
- йй —
cooling. This tendency was explained by Crow and Grimshaw by
showing that b is in reality a function of the temperature of the
powder gases *
Instead of assuming that the heating of the surface of the
powder to the ignition temperature results from molecular impact,
Kent [1935] suggested that radiation from the powder gases is
the cause. He argued that the escape of volatiles from smokeless
powder while it is being xvarmed up prevents contact of hot powder
gas with the surface, whereas radiation could penetrate to the
surface. He explained various experimental phenomena by this
hypothesis.
Ignition of powder at temperatures below the normal igni-
tion point by photochemical decomposition caused by the absorp-
tion of radiation of selected frequencies was suggested as a
possibility by Crawford [1937], in his proposal for experiments
involving the application of spectroscopy and photography to
interior ballistics. He also suggested the possibility of the
photosensitization of the ignition of powder by radiation from
cool mercury vapor emitting resonance radiation of wave-length
23/
253?A. Later Crawford remarked that the efficacy of potassium
in. promoting ignition might be explained as the result of emis-
sion of radiation of just the proper frequency by excited
potassium ions. He suggested that this^hypothesis could be test-
ed by exposing some powder to irradiated potassium vapor in an
evacuated tube.
23/ Maj. D. J. Crawford, Jr., Ordnance Department, personal
communication, Aug. 30j 19k1.
- U5 -
31. Quickness of powder
The rats of burning of a powder —- often referred to as its
quickness — is one of the most important factors in determining
the effectiveness of the powder for a particular purpose. The
criterion ’which is applied to the burning of a powder in a gun
is that a maximum proportion of the energy of the powder shall bo
transferred to the projectile without allowing the powder pressure
to exceed the limit imposed by the strength of the walls of the
tube. If the powder burns too fast, a dangerously high pressure
will be set upj whereas if the powder burns too slowly, some of
it will remain unburnod when the projectile loaves the muzzle,
and hence its energy will bo wasted. Tho rate of burning is con-
trolled by variation of the form and the dimensions of the grains,
particularly the web thicknoss. The smaller the web, the faster
will a powder bum, because for a given total weight, powder
grains with small web have a larger surface area.
Direct measurement of the quickness of a powder is now pos-
sible by a method developed at tho Burnside Laboratory of the
Du Pont Company. While a Sccmplc of the powder is being burned
in a closed chamber, an automatic oscillograph record is made
of dp/dt, the time-rate of change of the pressure, as a function
of the pressure. By comparison of this result with that obtained
with a standard powder, the ballistic properties of which had been
determined by firings in a particular gun, it is possible to calcu-
late the charge of powder required to achieve a desired velocity
in a similar gun.
- Ц6 -
The uniformity of the rate of burning is also important; for
if the rate is irregular, pressure waves may be set up in the bore
of the gun. Such waves are potentially dangerous, for by rein-
forcement of two of them, a pressure large enough to burst the gun
may be attained. Uniformity of burning is aided by proper design
of the ignition system, striving toward the ideal situation of
enveloping the charge of smokeless powder in a hot flame from the
igniter charge so that all the grains are ignited simultaneously.
2Ц/
32. Heat of explosion and heat of combustion
The heat of explosion of a propellent powder is the quantity
of heat evolved when the powder burns at constant volume in a
closed chamber without added oxygen. It is less than the true
heat of combustion, which is the heat liberated when the same
powder is burned at constant volume in an excess of oxygen. (Some
viritors, as for instance do Bruin and de Pauw [1928] , designate the
heat of explosion as the heat of combustion.) The heat of explo-
sion is of more practical interest, because it measures the
25/
potential of the powder — that is, its capacity for doing work.
24/ A summary of the heats of formation of the constituents
of propellants has been given by Schmidt [193й] and by Pike [19Ц2],
2$/ This definition of powder potential follows Hayes [1938.
p. 5ojT J. 0. Hirschfelder [personal' communication, Aug. 29,
19^2] supports an earlier suggestion by R. H. Kent in recommending
that the powder potential be taken as the product of T.,, the
adiabatic flame temperature (Sec. 36), and Cv, the high-tempera-
ture molal heat capacity of the gas at constant volume. This
change of definition is equivalent to considering Cv in the pro-
duct TeCv as the average value between, say, 2000°K and the
adiabatic flame temperature instead of as the average value be-
tween 0°C and the adiabatic flame temperature [compare Eq. (V-1)
in Sec. 36], The potential calculated in this way is sone 20
percent larger than the heat of explosion.
- и? -
MJ
In the calorimetric determination of the heat of explosion
the calorimeter is usually at or near room temperature, and there-
fore the water formed during the reaction is condensed and its
heat of vaporization appears as part of the apparent heat of ex-
plosion. To obtain the true heat of explosion (water gaseous) the
amount of water must be deterrained. The correction for the heat
of vaporization amounts to slightly less than 10 percent of the-
apparent heat of explosion (water liquid) [Noble 1906, pp. й?6-80;
de Bruin and de Pauw 1928, Tables III and IV].
Values for the heats of explosion and of combustion of a
number of powders appear in Table VII. The results of Dunkle
[1935] showed that the ratio of the heat of explosion Q to the
heat of combustion H of a smokeless povzder is a linear function
of the ratio of the number of molos cf atomic oxygen per gram of
powder to the sum of the corresponding numbers for carbon and
hydrogen [0/(C+H2)] in the powder; and also that it is a linear
function of the corresponding ratio [C02] »I.H20]/[C0] • [H2] of the
products of explosion of the powder. The slight variation of
27/
the heat of explosion with the density of loading [Noble 1906,
Plato 14], which is related to the question of change of composi-
tion of the products of explosion during coding, is discussed
in Sec. 39.
26/ Noble [1905, pp. 216-20]; de Bruin and de Pauw [1928,
1929]; Crow and Grimshaw [ 1931 a].
27/ The density of loading is the ratio of the weight of
charge to the weight of water that would fill the chamber at 4 °C;
hence in the metric system it is numerically equal to the weight
of charge in grains divided by "the volume of the chamber in
milliliters.
- 1x8 -
Table VII. Heat of explosion, heat of combustion and
temperature of explosion of propellent powders.*
Compositiona (percent by wt.)	Nitrocellulose Powders		Double-base Powders		FNH Powder
	N3	X-927**	C2	1511**	1358**
Nitrocellulose					
(12.6^ N)	900	95.23			
(13.21 N)			70.16	78.20	83.97
Nitroglycerin	———	———	28.6?	19.80	—
Dinitrotolueno	—	—	——	———	9.88
Dibutylphthalate	———	—— —	——		L.9U
D iphenylamine	o.U5	0.1x9	—-	0.99	1.00
Volatile matter	lx.75	Lx.28	1.17	1.01	0.22
Total	100.00	100.00	100.00	100.00	100.01
H(kilocal/gm)b	831	861	1220	1153	751x
Q(kilоcal/gm)c	——	2б11х	—	2377	2980
Temp. (°C)d	21x85	—	3U33	—	T—**
Temp. calc. (°C)4'	2Ц00	21x25	3300	3075	—
aSee Table IX for composition of products of combustion of
these same powders.
^Heat of explosion, water liquid.
Heat of combustion.
^Calculated by Crew and Grimshaw from heat of explosion and
heat capacity of pewdor gases.
“Calculated for this report from composition by method of de
Bruin end de Pauw [1929]. (J.S.B.)
'rCrow and Grimshaw [1931b].
^Dunkle [1935].
- 49 -
Table VIII, Products of combustion of gunpowder J*-5,
Loading^3 Pressure0	0.10 1.6		. o.5o 10.7		0.90 35.6	
Gases	Composition (percentage)					
	Wt.	Vol.	Wt.	Vol.	Wt.	Vol.
C02 CO H2 CH^ H2S	25.97 3.03 12.01 o.o5 0.06 O.lll	48.99 8.98 35.60 2.07 0.29 4.06	25.22 5.63 10.22 0.0? 0.16 0.66	47.21 17.04 30.29 3.01 0.84 1.61	27.50 3.56 10.85 0.03 0.15 0.77	52.65 Ю.73 32.64 1.27 0.81 1.90
Total	41.53d	99.99	41 .96	100.00	42,86	100.00
Solids	Composition (percentage)					
K2CO3 k2s2o3 K2sot K2S KCNS KNO3 (nhu)2co3 c Free S	30.07 11.66 11.71 2.30 0.00 0.32 o.o3 ’ 0.72 ' 0.41		35.20 14.70 2.69 2.06 0.17 0.29, 0,06 • 0.00 . ' 2.8'7		37.55 4.91 4.8? 4.13 0.21 0.11 0.09 0.00 5.27	
Total 	A	57.22,		58.04		57.14	
*After Noble qnd Abel [18?51, Tables 2, 3, 4. ^Large-grain rifle powder^ Waltham Abbey. Composition: KNO3, 74.95%; KsS0i , 0.15%; S, 10.2?%; charcoal, 13.52%; water, 1.11%.						
^Proportion of space occupied by the charge; not "density of
loading."
«
cLong tens per square inch.
^Should be 42.78% - error in original for one of the individual
percentages.
- 50 -
33. Products of combustion of gunpcwder
The composition of the products of conbustipn of propellent
ponders after explosion in a closed chamber have been determined
by various investigators. Noble and Abel [1875], for instance,
as a part of their classic research on Fired gunpowder analysed
the products of combustion of several kinds of gunpowder at
different densities of loading. Their results for a representa-
tive gunpowder at three densities of loading are given in Table
VIII.
Over half the weight of the material is solid, which is
responsible for the smoko from burning gunpowder. Among gaseous
products the volume percentages of nitrogen and of carbon dioxide
are much greater than from colloidal powder, whereas the percent-
ages of carbon monoxide and of hydrogen are much less (compare
Tables VIII and IX), These differences reflect the higher nitro-
gen and oxygen contents cf gunpowder as compared with smokeless
powders.
Table IX.
Products of combustion of smokeless povrders, in
moles per kilogram of powder, Table VII, in which
these powders are listed in the same order, gives
their composition.
Product	Nitrocellulose Powders		.Double-Base Powders		FNH Powder
	N3*	X-927*	02*	1511**	1358**
C02	3.200	5.2Ц2	6.607	8.322	3.292
CO	20.21Ш	16Л8Ц	12.771	11.704	2O.5U3
' Ha0	8.82?	5.922	11.272	7.923	5.001
N2	u.269	5.242	5.195	5.604	5.894
H2	6.979	8.219	1.676	5.120	9.139
*Crow and Grimshaw [ 1931b] .
*H!Dunklc [1?35] • Density of loading, 0.12.
- 51 -
3t. Products of combustion of smokeless powder
Because smokeless powder burns without leaving any appreciable
solid residue, the determination of its products of combustion is
just a specialized application of the standard technic of gas analy-
sis. The water formed during combustion, after it has condensed
in the explosion chamber, is cither wiped out and v/eighed as liquid
water [Noble, 1905, p. 203], or else it is distilled out of the
bomb and absorbed [de Bruin and de Pauw, 1928, p. 9], which is pre-
ferable. Analyses of the products of combustion obtained from
different kinds of smokeless powder have been published by Sarrau
and Vieillc [188Ц], by Noble [189h], by Macnab and Ristori [189Ц,
by Noble [19O6] and by de Bruin and de Pauw [1928]. A number of
unpublished reports from Picatinny Arsenal [Valente, 192 9; Dunkle
and Volsk, 1932; Volsk and Dunklo, 1932; and Dunkle, 1935] contain
analyses for the new FNH powders, and also for some experimental
powders of special compositions. A selection of results from
Dunkle [1935] at a density of loading of 0.12 is given in Table IX
in tho columns headed X-9273 1511 and 1358.
The variation in composition of powder gases with change of
density of loading is illustrated by the results of Noble, some of
which are reproduced in Table X. h'horeas the amounts of nitrogen
and of wator show only slight variation with density of loading for
all three powders, the amount of carbon monoxide decreases while
that of carbon dioxide increases as the density of loading, and
hence the pressure, is increased. Similarly the ratio of methane
to hydrogen increases very greatly with increase of density of
Table X* Variation in composition pf powder gases with change of
density c-f iouding.’^ ' “
A. Composition of powders, in percentages by weight.
Component''^	NC	C-I	C-M.D.
Nitrocellulose (sol.)	85.5	37.0	63.o
Nitrocellulose (insol.)	1h.5		
Nitroglycerin		38.0	30.0
Mineral jelly (vaseline)		5.0	3.0
B, Pressure and volume of gas.
Density of Loading	Pressure . (atnos)			Total Gas . (ml/gm)			Permanent Gas (ml/gm)		
	_ж_	C-I	C-M.D.	.110	C-I	c-e.o.	... NC	C-I	C-M.D.
o,o3	h37	h93	h37	993.1	870.0	933. h	81Ц.7	670.0	781.8
.10	973	1066	990	980.0	878.3	9h8.O	810.5	692.5	790.0
.13	1З16	1783	1600	938.3	880.0	931.0	795.0	699.0	786.5
.20	2103	2391	233h	93h.O	873.3	913.5	776.0	697.0	773.0
.23	2789	3h67	3193	906.3	863.0	893.5	751.5	688.0	75h.O
.30	3h98	hhoh	ho6?	883.0	8h8.O	873.0	730.0	671.5	733.5
.hO	3228	6302	3830	8h1.0	820.0	832.0	695.0	6hh.9	693.5
.30	7133	812Ц	73hh	802.0	798.8	789.3	659.5	623.6	653.5
*After Noble [1901, pp, Ш-7, h80].
NO, nitrocellulose; C-I, cordite Mark I; C-M.D,, cordite
M.D.
[Table X continued cn next page,]
- 53 -
TABLE X. (Continued.)
G. Total composition in percentage by volume.
Density of Leading (gm/ml)	o.o5	0.10	o'.i5	i o.2o| 0.2$	0.30	o.ho	o.5o
I. Nitrocellulose
co2	111.95	16.19	17.50	19.110	21.50	23.50	27.60	31.60
co	35.36	3h.6O	33.35	31.90	29.95	28.25	211.65	20.96
H	20.01	20.67	19.90	18.00	15.80	ili.o5	11.60	10.00
CHU	O.h9	0.71	1.58'	2.89	li.8O	6.20	8.I1I1	9.80
N	11.19	10.75	10.62	10.83	11.011	11.16	11.00	11.00
H20	18.00	17.08	17.05	16.98	16.91	16.8a	16.71	16.611
Total	100.00	100.00	100.00	100.00	100.00	100.00	100.00	100.00
IT. Cordite Lark I
co2	21.07	21 .98	23.13	211.37	25.8?	27,611	30.56	32.118
co	26.116	26.13	25.20	23.91	22,31	20,1111	17.116	15ЛЗ
H	13.53	15.12	15.60	15.53	111,96	13.93.	11.73	9.117
снц	0.23	0.32	o.51i	1.00	1.65	2,115	3.98	5.51i
N	15.97	15.08	111.93	111.86	111.90	111.95	15.11	15.60
H20	22.7I1	21.37	20.60	20.33	20.31,	20.59	21.16	21.118
Total 	.		100.00	100.00	100.00	100,00	100.00	100,00	100.00	100.00
III. Cordite M,D.
C02	111.85	16.115	18	35	20.30	22,25	211,15	28.15	32.35
CO	311.87	33.95	32	hO	30.50	28.115	26.115	22.60	19.00
H	18.95	19.20	19	00	18.00	16.65	15.00	11.80	8.115
СНц	0.29	0.83	1	60	2.70	3.95	5 .Цо	7.во	9.95
N	12.89	12.57	12	115	12.50	12.65	12.85'	13.05	13.1.15
нго	18.15	17.00	16	20	16.00	16.05	16.15	16.60	16.80
Total	100.00	100.00	100	00	100.00	100.00	100.00	100.00	100.00
- 5Ь -
loading. The cause of these variations is considered in Sec. 39
in connection with a discussion of the gaseous equilibria exist-
ing at the temperature of explosion.
33, Composition of powder gases from a gun
The experiments that have boon referred to so far were per-
formed with closed chambers. A few analyses have been made, how-
ever, of the gases formed in an actual gun. Thus Noble [1906,
pp. h.55-6] obtained the results shown in the second column of
Table XI by analysis of a sample of gas withdrawn from the breech
end of a 9.2-in, gun just after it had fired a charge of 103 lb
of cordite, giving a pressure of 16.1 tcns/in? and a muzzle velo-
city of 2б00 ft/soc. For comparison, tho last two columns of this
table give Noble’s analyses of the gases obtained from firing
charges of cordito at a density of loading of 0.05 in a closed
chamber, which in one case had been exhausted and in the other had
been initially filled with air at atmospheric pressure. The com-
position of the gases in the gun agrees closely with those in the
closed chamber. Poppenbcrg and Stephan [1909b] found from an
analysis of gaseous mixtures taken at various parts of the barrel
that there is more carbon monoxide t the moment of explosion than
there is after the gases have cooled down.
The presence of'considerable quantities of iron in the powder
gases was claimed by Siwy [1908], but he published no supporting
evidence. He did not even describe the method of detection.
-Sa-
lable XI, Products of combustion of cordite in a gun.
compared with those obtained in a closed
chamber, in percentages.
Product	Gun (Mean of Two Rounds)	Closed Chamber	
		With Air	Evacuated
co2	25.6	г?.15	26.35
CO	35.8	3U.35	35.05
H	19.0	17.50	19.50
CHU	0.5	о.зо	0.60
N	19.1	20.70	18.50
Total	100.0	100.00	100.00 .•
36,	Explosion temperature
28/
The theoretical explosion temperature refers to the tempera-
ture to which tho products of an explosion would be raised if the
reaction took place adiabatically. This temperature on the centi-
grade scale is
TG * Q/CVJ	(V-1)
where Q is the racial heat of explosion at constant volume (referred
to products cooled to 0cG), summed over all the components of the
original explosive, and Gv is the mean racial heat capacity from 0
to TcC, summed ever all tho products of the explosion. Calcula-
tions of the explosion temperature based on this aquation arc dis-
cussed in the next section.
Various attempts have boon made to measure the temperature of
explosion directly. Noble and Abel (1875; p. 1?1 in 1906 reprint]
28/ Also called adiabatic flame temperature.
- $6 -
showed that the temperature of explosion of gunpowder is higher
than the melting point of platinum, by firing a very thin sheet
of platinum and a coil of fine platinum wire with large charges
of gunpowder in a closed chamber. Portions of the wire were weld-
ed to the sheet, and the-, shoot itself showed the beginning of
fusion'when examined under a microscope.
Measurement of the explosion temperature of smokeless powders
by means of thermocouples was attempted by Macnab and Ristori
[1900J . Because the . heat losff is so groat, the naxfiw-l tempera-
ture recorded by a platinum-p^atinrhodium thermocouple in a closed
chamber depends on the diameter of the wire. Each couple of a
series of ten made of wires ranging in diameter from 0.010 to O.OhO
in. was used to measure the temperature of explosion of the same
charge of powder under the sane conditions, The enf of the galva-
nometer was recorded as a function of time on a fixed photographic
plate fitted with a moving slit. The maximum deflection was given
by the couple made of the thinnest wires; the deflections of the
others wore progressively less. It was hoped to extrapolate the
deflections to a thermocouple of zero thickness, and to calibrate
them in terms of temperature; but the attempt was not entirely
successful* It was demonstrated that the explosion temperatures
of the three explosives, guncotton, cordite, ballistite, increased
in the order named, which is the same order as that obtained from
calculated temperatures.
It has been suggested that explosion temperatures might be
- 57 -
29/
measured by means of the spectra of the burning gas, a method
that has been discussed recently by Brinkman [i9ho], The line-
reversal method has been used successfully in measuring the
flame temperatures in the internal combustion engine. It was
suggested by Lewis and von Elbe [1938д p. 337] that this method
might be adapted to the measurement of the explosion temperature
in a closed chamber ”by suspending highly dispersed sodium salts
in explosion mixtures and recording the reversal point photographi-
cally by progressive adjustment of the comparison radiator.’1’
37.	Explosion pressure
The explosion pressure is the maximum pressure that would be
developed by the powder gases if the reaction took place adiabati-
cally in a closed chamber. It is related to the temperature of
explosion TQ by the equation of state of the pewder gases. At the
high temperatures of explosion, the internolecular attraction term
in the equation of state can be neglected, and the following simple
form of equation suffices:
Po (v-oc) = RTg,	(V-2)
where v is the specific volume of the powder gases at the pressure
P , a. is thoir average cuvplume and R is tho gas constant per gram.
29/ Thu temperature of the powder gases burning inside a
closeTchamber has been determined recently at tho Geophysical
Laboratory by measuring with photoelectric cells the intensity
of radiation -in different parts of the spectrum that is transmit-
ted by a quartz window in the side of the chamber. This technic
will bo described by F. 0. Kracek, ff. Benedict and L. G. Bonner
in a forthcoming NDRC report.
- 58 -
3£/
Since the density of loading A is the reciprocal of v, this equa-
tion nay be written in the form
Pe = ДНТэ/(1	(V-3)
Since ex. is approximately 0.001 for the six gases commonly found as
products of combustion of powder [Sarrau, 1893; Burlot, 192Ц], the
explosion pressure increases almost linearly with an increase in
density of loading. Because the number of moles of gas per gram
of powder depends on the gas composition, the constant R for a
given charge also depends on tho composition.
Because of the rapidity with which the powder gases lose their
31/
heat to the walls of the chamber, the pressure measured in a
closed chamber never quite attains the theoretical maximum. For
the same reason it is doubtful whether tho adiabatic explosion
temperature is actually reached. Some of Noble's experiments [1905.
P. 227] demonstrated the extreme rapidity of cooling. Thus the
pressure of the powder gases from cordite fired in a closed chamber
decreased from 39,000 Ib/in? to 60 percent of that value in 1 sec.
The loss of pressure is greater at a low density of leading. Noble,
nevertheless, did not correct the observed pressures, and hence his
measurements — some of which are reproduced in Table X,B — show
considorable departure from linearity at low densities of loading
30/ This relation assumes that the weight V/ of tho powder
gases is the same as the weight of the original charge, Then
v = V/U, and in the metric system, A is numerically equal to
W/V, where V is the volume of tho chamber (see footnote 27).
The expansion of the chamber by the pressure is neglected.
31/ See Chap. X for methods of measurement.
- 59 -
and approach linearity at high densities. He had previously cone
to the conclusion [Noble and Abel, 18?5] that the pressure loss
due to the cooling would not exceed 1 percent. However, the spe-
cial experinents of Muraour [1923, 1925a, and 1925b] and of Crow
and Grimshaw [1931b] have shown that this loss nay easily exceed
10 percent, especially at low densities of loading or in a snail
chamber.
In a gun the conditions are much more complex than in a
closed chamber, because of the expansion of the gases as the pro-
jectile moves forward. They will be considered in Sec. 50 in con-
junction with a discussion of the movement of the projectile.
38.	Approximate calculation cf temperature of powder gases
The temperature of the powder gases at the tine of explosion
may be calculated by either of two independent methods, which aro
based on Eqs. (V-1) and (V-3), respectively. The former is related
to the thermochemical properties cf the powder and of the evolved
gases. Equation (V-1) seems to have been used first for this pur-
pose by Mallard and Le Chatelier [1883]. Equation (V-3) was devel-
oped by Abel as an empirical relation in the form
P = XA/(1 - a A) ,	(V-h)
where A and oc were empirical constants, and it is often referred
to as the Abel, or the Noble and Abel, equation.
The calculation of the temperature of explosion from the maxi-
mum pressure developed in a closed chamber, in accordance with Eq.
(V-3), involves two difficulties. The equation itself is only an
approximation, and there is not at present sufficient knowledge of
- 60 -
tho kinetic properties of gases under the conditions of tempera-
ture and pressure concerned for it to be improved. Tho covoluno,
in particular, is imperfectly known. An equally important diffi-
culty is that of measuring the true pressure of the explosion.
As already mentioned, tho gas is cooled sc quickly by the walls
of tho chamber that the maximum- pressure measured is somewhat less
than the true pressure. The correction to bo added to the observed
pressure was evaluated by Muraour [1923, p. 323; 1925a, p, h60]
from experiments in a closed chamber in which the area of the sur-
face exposed to the gases could be varied. It was calculated by
Crow and Grimshaw [1931а» P« 50] as an example of heat conduction,
from pressures measured in two chambers of widely different sur-
face areas.
In the early applications of Eq. (V-1) to the calculation of
the temperature of explosion, Cv was evaluated on the basis of the
composition of the cooled powder gases. It was expressed as a
linear function of the temoerature; vrhoreupon Eq. (V-1) could be
32/
solved for T. It was soon realized, howeverthat the products 
of combustion found in a closed chamber after it has cooled to
room temperature are not necessarily the same as those present
under the conditions of high temperature and high pressure exist-
ing at tho time of the explosion, and also that thq heat capaci-
ties of gases at high temperatures are not linear functions of the
temperature.
32/ Seo Hayes [1938» p. 53] for an exposition of this
s olution.
- 61 -
39.	Secondary reactions during cooling
Experiments intended to elucidate the changes that take
place during cooling of the products of the explosion were con-
ducted by Poppenberg and Stephan. They confirmed Noble’s ob-
servations (see Table X) that the ratio
к = £Hs0] • [CO]/[CO2].’[H2]
decreased with increase of density of loading. They explained
this variation by the assumption that the mixture cooled more
slowly at high densities of loading, and hence that the "water
gas" reaction [Eq. (V-6)] had more time to proceed. This view
v/as substantiated by firings [Poppenberg and Stephan, 1909a]
made at the same density of loading with the explosion chamber
cooled to -120°C in one case and heated to 90°C in the other.
More carbon dioxide was produced at the high than at the low
temperature.
The formation of methane was shown to be a secondary re-
action by later experiments made by Poppenberg and Stephan [19*1 On]
and by Poppenberg [1923]. bi some of them the explosion took
place inside a small porcelain bomb contained in an evacuated
chamber. The sudden expansion of the gases when tho porcelain
bomb burst so cooled them that the equilibrium 'was frozen.
Criticism by Kast [1910] of the interpretation of those results
was met by a further discussion by Poppenberg and Stephan [1910b].
Their conclusion with respect to tho secondary formation of meth-
ane was confinaed by Muraour [1919a], who quenched the equilibri-
um mixture by having it expand through a 1-m canal into an evac-
uated vessel. It also is in agreement with the latest calcula-
tions [Kent, 1938a].
- 62. -
bO, Calculation of corrections for composition of powder gases
After it was realized that the composition of the cooled gases
reflected secondary reactions during cooling, methods of calcula-
tion were developed to correct for then. These corrections, com-
bined with improved,data for heat capacities of gases at high tem-
peratures and with increasingly precise measurements of explosion
pressures, gradually decreased the discrepancy between the values
of explosion temperatures calculated from the maximum pressure and
those calculated from heat capacities. At first [Noble, 1906, pp,
Ц63-5; Popponberg, 190.9; Muraour, 1919b] the temperatures calcu-
lated from the maximum pressure were much too low, except at-high
densities of loading. In a later comparison [Muraour} 1g2ba,
1g2bb, 192bc, 1926] the disagreement was much loss.. Finally the
very thorough investigation of Grow and Grimshaw [1931b] resulted
in agreement within 2 percent for the value of X — tho ballis-
tic force of the propellant — derived from the heat capacity and
heat of explosion and that derived from direct measurements of the
explosion pressures at different densities of loading. This func-
tion is.the leading coefficient in the equation of state adopted
by Crow end Grimshaw,	'	.
Po = A (A + «.А3 + a«.3A3 +	(V-5)
v/hich is merely a more elaborate form of the Noble and Abel equa- 
tion, Eq, (V-b).
The mpthod of calculation used by do Bruin and de Pauw [1928]
and by Schmidt [192g] tc correct for the change in gas composition
by tho secondary reactions in cooling consisted in calculating the
- 63 -
corrections to tho ’composition of the cooled, leases, by application
33/
of the equilibrium constant for tho secondary water-gas reaction,
CO + H20	C02 + H2.	(V-6)
3h/
111, Calculation of temperature and composition of powder gases
Tho method of Henderson and Hasse [1922], which was later used
by Poppenberg [1923] and by Crow and Grimshaw [1931b], is superior
in that it dees not require a knowledge of tho composition of the
cooled gases. By a series of successive approximations the equi-
librium composition of the hot gases is derived from the following
experimental data: (i) the molal heat of explosion at constant
volume; (ii) tho chemical composition of the powder in terms of the
chemical elements present; (iii) the equilibrium constant as a func-
tion of the temperature for each of the reactions in which the pro-
ducts of combustion may be assumed to participate; and (iv) the
mean molal heat capacity from 0cC to the explosion temperature for
each of the substances that it is assumed might be present in the
explosion.
The molal proportions of tho chemical species assumed to
participate in the equilibria at the temperature of the explosion
33/ For a discussion of this reaction, particularly in
flames, see Bono and -Tovmsend [ 192 7 j Р» 322].
3h/ Hirachfelder, McClure and Curtiss [19112 j have systema-
tized the calculation of the adiabatic flame temperature and the
composition of the powder gas. Their method is based on the same
data, as is the one described in Sec. ill; but instead of carrying
out the approximation by assuming successive values for the flame
temperature, they calculate the energy loss at two different
assumed flame temperatures, and then, by linear interpolation be-
tween these values for that flame temperature which would corre-
spond to zero energy loss, they obtain the true flame temperature.
- 6Ц -
form the unknowns of a series of simultaneous algebraic equations.
Ona group of these equations of condition is based on the known
chemical composition of the powder. The other is derived from the
equilibrium constants for the assumed equilibria, evaluated at a
provisionally assumed temperature. The solution of these simul-
taneous equations gives the first approximation to the molal com-
position at the time of explosion. (Henderson and Hasse con-
sidered only the water-gas reaction in the main calculation, and
thon used the equilibrium constants for various other possible re-
actions to obtain second-order corrections.) From this result and
the assumed temperature, tho mean molal heat capacity Cv of the
whole mixture is calculated, and then tho experimental value for
the heat of explosion is divided by Gv to compute tho temperature
[Eq. (V-1)]. This value of the temperature, ’which will differ
somewhat from that originally assumed, is used as a basis for a
repetition of the calculation. Finally, after one or more repeti-
tions, the computed temperature will agree with tho assumed tempera-
ture. This value and tho corresponding molal composition are con-
sidered as those of the burning gases.
This method of calculation, which involves the simultaneous
consideration of a number of equilibria, was used by Kent [1938a]
in a recalculation of the composition of the gases from two of
the powders previously considered by Crow and Grimshaw [1931b].
The equilibria involving the formation of methane and nitric oxide
and those for the dissociation of -water and nitrogen were included
in addition to the water-gas reaction, which had been tho only one
- 65 -
35/
considered by Grow and Grimshaw, This recalculation made use
of the latest values for heat.capacities of gases at high tempera-
tures, obtained largely from measurements of band spectra [David
and Leah, 193U; Lewis and von Elbe, 1938, Chap. XVI]. The results,
which are reproduced in. Table XII, show that the early assumption
of the dominance of the water-gas reaction was correct. Later un-
published computations [Kent and Lane, 19Ц1] involving a total of
twelve different equilibria have not changed the results materi-
ally.
The water-gas reaction does not involve a volume change if
the gases are ideal, and hence the equilibrium is not affected by
change of pressure. On this basis it has boon argued that the
apparent change of explosion temperature and of heat of explosion
with variation in density of loading arc spurious effects. The
existence of reactions involving volume changes in the powder
gases, however, brings in a slight variation of the. explosion
temperature with change of pressure, as shown in Table XII.
h.2. Equilibrium conditions during burning
Although the calculations just discussed furnish us with our
best knowledge of the composition and temperature of powder gases
at the time of explosion, there remain two possible sources of
uncertainty, in addition to the uncertainties of the experimental
data involved in the calculation. The variation of the heat ca-
pacity of the gases with pressure [Muracur, 192ца, p. 330] has
35/ Hirschfaldor, hicClure and Curtiss (reference Зй) have
repeated the calculation, using a variation of this method with
the additional refinement of correcting for the fact that the gas
is nonideal.
- 66 -
Table XII. Partial pressures, in atmospheres, of the
constituents of powder gases, and tempera'
ture of explosion.
Powder	Nitrocellulose		Ballistite	
Pressure (atmes)	3U0	3U00	3U0	3U00
CO	138.Ц8	1386.5	81.0U	756.8
C02	UO.92	U11.0	73.86	827.5
H20	82.00	827.9	88.89	96U.8
n2	36.17	326.6	50.8U 	52.2.5
H2	ЦО.69	U07.U	12.60	111.2
02		——	5.08	26.0
N	0.01	—	0.17	1.3
H	.8U	2.9	3.11	-16.1
0	.01	—	1.76	7.2
OH	1.02	3.5	18.99	133.9
NO	0.06	0.2	3.86	3U.7
Temp.(°C)	2663	2689	3398	368U
*Aftcr Kent [1938] .
not been taken into account. Moesveld [1928, p. 3U] concluded,
however, on the basis of the van de? Vfaals equation, that the
variation is negligible at high temperatures.
The other source of uncertainty, namely, tho assumption of
a state of equilibrium among the atoms of a gas, is more impor-
tant, because this assumption underlies all the calculations,
Muraour [l92Ua, p. 335] suggested that during combustion equilib-
rium may nut be maintained^ oxygen, for instance, may react more
rapidly with hydrogen than with carbon. He considered, never-
theless, that equilibrium would be established as soon as burn-
ing was completed.
- 67 -
Lewis and von Elbe [1938, p. 306] pointed out that in the
absorption of the energy of explosion by the gas molecules there
maybe a lag in the excitation of the translational degrees of
freedom of carbon dioxide, carbon monoxide and nitrogen. The
resulting momentary excess of translational energy causes "a
higher pressure which lasts for a period comparable with explo-
sion times. Ultimately, energy equilibrium among all tho degrees
of freedom is established. Thus, tho heat capacity of those
gases is a time function." A somewhat similar possibility of
nonoquilibrium conditions is that suggested by Crawford [1937],
who considered that because of the very rapid rate of burning
in a gun, tho gas kinetic energy of tho products of combustion
lags behind the radiant energy field of the explosion system.
This would cause a considerable deviation from tho van der
Waals equation.
An investigation of equilibrium has been made recently at
Aberdeen Proving Ground in collaboration with Professor H, C,
Urey [Kent and Lane, 19^1]. A small amount of barium carbonate
containing a heavy isotope of carbon was fired with a charge of
powder, and then the distribution of the heavy isotope between
carbon monoxide and carbon dioxide was determined in the pro-
ducts of tho combustion after they had been quenched by rapid
expansion. According to a preliminary report of these experi-
36/
ments, the heavy isotope was found uniformly distributed
36/ R. H. Kent, personal communication to R, E. Gibson,
Jan. 19U2.
- 68 -
between the two gases. This is considered as evidence that
chemical equilibrium had been reached during the combustion
of the powder.
- 69 -
CHAPTER VI. MOVEMENT OF THE PROJECTILE IN THE- BbRE ’
Ths detailed mathematical description cf ths movement of
the projectile in the boro of a ;gun, which is one of tho princi-
37/
pal problems of interior ballistics, is too involved to be pre-
sented in this report. Instead, a few outstanding details of
that description will be mentioned in their relation to erosion.
hU. Rate of increase of pressure
The rate at which the pressure increases behind a projec-
tile in a gun depends on the interaction of several factors.
It is controlled principally, of course, by tho rate of burning
of the powder, but this reciprocally depends on the pressure.
In a closed chamber the pressure rises at an ever-increasing
rate until the powder is nearly all burned. In a gun, however,
tho rate of increase of pressure is partly checked by the in-
crease cf volume caused by the movement of the projectile. At
first the expansion is slow, because tho pressure is low and also
because the resistance to movement of the projectile is high until
the rotating band has been engraved by the rifling (soe Sec. Ц6).
Later tho expansion is fast enough to offset partially tho in-
creased rate of burning cf the powder. Next the amount of burn-
ing powder becomes so small that the evolution of gas begins to
37/ The Le Luc equation for the velocity of the projectile
in the bore, which is used in designing new guns, is described
in Hayes [1938, pp. 7U-81] and in Naval ordnance [1939, pp.
50-85]• A more refined form of senienpirieal calculation is
afforded by the use of tho Tables for interior ballistics pre-
pared by Bennett [1921].	'
- 70 -
decrease. This effect combines with the over-increasing expan-
sion to cause the rate of increase of pressure to become zero.
After the attainment cf a maxinun pressure, the remainder of
the powder is burned within a short interval of time during which
the pressure decreases slowly. Finally the pressure continues to
decrease approximately as in an adiabatic expansion. The curves
of pressure versus time for several guns (Fig. 1) clearly show
those variations cf the pressure. They arc photographic records
made by means of a cathode-ray oscillograph attached tc a piezo-
electric gage during the firing of actual guns.
Position of projectile at maximum pressure
Although the time required for the pressure to build up to
a maximum is a considerable fraction of the total time the projec-
tile is in the bore, up to the moment of maximum pressure the pro-
jectile has moved only a few caliber lengths from its initial posi-
tion. At the time of maximum pressure that part.of the bore of the
gun between the breech and tho base of the projectile is subject
to tho maximum pressure. After that the pressure decreases slow-
ly as the projectile continues tc move toward tho muzzle. The
muzzle pressure, the exact value of which depends on the speed of
burning of the powder and on the length of the tube, is of the
order of one-fourth the maximum pressure.
38/
h-6. Friction of the projectile in the bore
W
Both static and dynamic measurements have been made of
4-t------------------;........................................ .
38/ See Soc. 53 for heat of friction.
39/ Some of the earliest static measurements were made at
Watertown Arsenal with the "United States Testing Machine" and wore
reported in Tests of metals published annually by that Arsenal*

Г> S'S'&-/с/	’/ '^/_j/
- 72 -
the initial resistance of the projectile to movement, caused by
the work required to engrave the rotating band — or the soft
metal jacket, in the case of a bullet — and the subsequent fric-
tion between the boro and the two parts of the projectile that
touch it, namely, the rotating band (Sec. 18) and the bourrelet
(Sec. 17). bi one case, for instance, the resistance in a worn
75-nm gun, M1897 (fired 7755 rounds) was found to be I4.0,000 lb
at the origin of rifling and about 15,000 lb at the muzzle [Ord.
Dept., 1922b]. Tho actual resistance to a moving projectile,
however, is probably much less than the result of such a static
measurement. This was indicated by the fact that when projec-
-tiles having rotating bands of reduced diameter wore fired from
a 21i0-mn howitzer, practically no effect on pressure or velocity
was found [Ord. Dept., 1922a]. this conclusion is in agreement
with the suggestion of Justrow [1923] that the friction between
the band and the bore corresponds approximately to that of a
piston adjusted for suction.
A summary of several dynamic methods of measuring bore fric-
tion has been given by Kutterer [19^2]. In Cranz' method a shot
is fired from a shortened tube from which it initially protrudes
about one-third its length. The engraving resistance is taken
equal to the mean pressure corresponding to a series of equal
charges which are just sufficient to eject the projectile about
half the time. In several other methods the frictional force
is evaluated as the difference between the force tending to push
the projectile forward and the force of recoil. In Sebert’s
method the frictional force is evaluated as the difference be-
tween the force acting on the projectile and that acting on a
- 73 -
frictionless piston inserted in on axial hole through the shot.
These two forces are measured by differentiation of two space-
time curves obtained by means of recording tuning forks on
frictionless slides attached to the shot and the piston.
Liebessart improved Sebert’s method by measuring the displace-
ment optically.
The method of Cranz and Schardin [1932] utilizes a breech
block consisting of a heavy frictionless piston, having the same
area as the projectile, so that the forces on them are the same.
Hence, when the gun is fired from a free recoil carriage, the
tube is pulled forward by the frictional drag. The.frictional
force is the product of the mass of the tube and its accelera-
tion. The latter is obtained by tho double differentiation of
the space-tine curve for the tubs’. Kutterer [19h2] modified
this method by measuring the acceleration of the tube directly
by attaching to it. a frictionless piston which registered
against a piezoelectric quartz gage.
The methods mentioned have required a modification of the
operation of the gun or projectile. Tho friction of a standard
projectile in the bore of a 1h-in. Navy gun was determined in-
directly during an investigation of the ballistics of this gun
[Bur. Stand., 192 Ца] . The pressure on the base of the projec-
tile computed from the acceleration of recoil was less than the
gas pressure in-the chamber measured with a. spring pressure gage.
Цо/
This difference was considered a measure of tho friction.
ЦО/ Preparations are being made for application of this
methoa to measurement of the friction and also other ballistic
properties of several guns of moderate caliber, under the super-
vision of.H, L. Curtis of the National Bureau of Standards, for
Section A, Division A, NDPC.
- 7h -
kl/
A direct-reading gage has been suggested recently by Smith
[19h2]. It consists of a quartz piezoelectric gage mounted in
the base of the projectile and connected to an oscillograph by
means of a wire that comes out the muzzle of the gun.
UY* Relation of friction to erosion
The divergent views concerning the influence of the rotat-
ing band on erosion have already ^en mentioned (Sec..19). The
magnitude of neither that influence nor that of friction between
the bourrelet and the bore has been evaluated. Nonsymmetrical
U2/
muzzle erosion has been ascribed to the wear between the
bourrelet and a particular land with which it remains in contact
during most of its path down the bore.
It is generally agreed, however, that the amount of erosion
caused by friction between the projectile and the bore is greater
in small arms than in guns firing projectiles vd_th rotating bands.
The difference between the erosion in the two kinds of weapons,
however, seems to be merely one of degree rather than of kind.
This point of view was emphasized by Greaves, Abram and Rees [1929,
p. 158], who suggested that although the total amount of metal
eroded per round increases with caliber (sec Table XVIII), a
smaller proportion is removed by friction in the larger guns. This
Ц/ This gage is now being used in a series of measure-
ments with a 3-in. gun at Aberdeen Proving Ground under the
auspices of Section A, Division A, NDRC. See Crocker and Smith
U2/ Arthur E. Jewell, Gage Section, Aberdeen Proving Ground,
personal communication.
- 7$ -
conclusion is based on the fact that the force applied to unit
area of the surface of contact between the rotating band and the
bore is about the same for all guns fired at the sane pressure,
whereas the heat input to unit area of the bore surface increases
very rapidly — because the ratio of the weight of charge to bore
surface increases linearly — with an increase of caliber.
Il8. Velocity of the projectile in the tube
The velocity of the projectile continues to increase as the
gases expand after the tine of maxinum pressure. Noble invented
the chronoscope for the determination of the velocity at different
points down the tube by recording the tines when the projectile
passed these points. In the original arrangement described by
Noble and Abel [187!?], the tube of the gun was drilled at a
series of points along its length. Each hole was fitted with a
plug which carried a wire arranged in such a way that it was cut
when the projectile passed that point. Cutting the wire inter-
rupted the primary current of an induction coil, whereupon a
spark recorded itself on a piece of paper attached to a disk,
36 in. in circumference, that was rotating with a constant speed
of about 1250 rev/min. The instrument was capable of recording
the millionth part of a second, and when it was in good working,
order, the probable error of a single observation did not exceed
h or 5 x 10"6 sec. nfter the distance of travel of the projec-
tile had been expressed as a function of tho tine, the velocity
and the pressure were computed by two differentiations. A some-
what similar contacting arrangement was used at Aberdeen Proving
- 76 -
Ground [Kent and Hitchcock, 1923] in a study of tho internal
ballistics of a.2U0-mm howitzer» A scries of 13 contacting
plugs were connected to an oscillograph to obtain a direct tine-
travel record,
1x9. Muzzle velocity and energy
The nuzzle velocity of the projectile, which is an impor-
tant characteristic of the gun, is determined by measuring with
43/
a chronograph the time required for the projectile to pass be-
tween two velocity frames set up at measured distances in front
of the gun, and then applying a correction to take care of the
small change of velocity between the nuzzle and the point of
measurement. For the first 10 yd or so tho velocity is increased
by a few feet per second by the rush of the escaping gases, and
then it decreases. The muzzle velocities of the guns in use to-
day generally range from 15OO to 3000 ft/sec at full charge. If
the full range is not needed, sone of then, howitzers especially,
are fired at reduced charge, which yields a lower muzzle velocity.
The muzzle energy, which is a measure of tho poxver of the
projectile, is determined by the nuzzle velocity, the velocity of
rotation and the mass of the projectile, Tho proportion of the
powder energy represented by the muzzle velocity is the thermo-
dynamic efficiency of the gun. This efficiency is about 30 per-
cent, as is shown in Table XV (Sec. 92). The mechanical effi-
ciency of a gun, considered as the ratio of the muzzle energy to
1x3/ See Ordnance Dept. [1936, No. 1x0-17] for a description
of the procedure of this measurement.
- 77 -
the work represented by the area of the ideal indicator diagram,
was calculated by Henderson and Hasse [1922p, Ц73] as 8h to 90
percent for a number of British грдпз fired with cordite M.D. at
nuzzle velocities of about 2700 ft/sec.
So, Effect of expansion of powder gases
Although the pressure in a gun firing a service round is
about the sane as in a closed chamber at a density of loading
of 0,20 to 0,2$ (see Tables I and X), the gases in the two en-
closures arc not subject to the sane conditions up to the
moment of maximum pressure. In the closed chamber this pressure
is attained without the performance of any work by the gas, where-
as in the gun the gas expands at the same tine that the pressure
increases. Because the secondary water-gas reaction [Eq, (V-6)]
involves no volume change if the gases are ideal, this expansion
has less effect oh the gross composition of the powder gases
than it otherwise night. On the other hand, a possibility which
nay be of special significance in connection with erosion is that
the expansion may promote some reaction that is affected by the
change of pressure, and thereby cause the. formation in the gas
mixture of a chemical combination that might readily react with
tho steel bore.
Another possible cause of a local disturbance of the gase-
ous equilibrium is the cooling of the gas. In a 3-in. antiaij>-
craft gun, for instance, the cooling has been found by calcula-
tion to be about 1000°C by the tine the gases reach the muzzle,
which corresponds to a .gradient of about 3° рог centimeter
- 78 -
Ы±/
travel of the projectile. Most of this cooling is caused by the
work performed in pushing the projectile down the bore. Because
it affects the mass of gas as a whole, any change of composition
resulting from this part of the cooling is distributed uniformly.
Part of the cooling, however, is caused by contact of some of the
gas molecules with the cold surface of the bore; and this change
is not uniform. Not only is the cooling confined to the layer of
molecules adjacent to the wall of the bore, but the return of
these molecules to the main mass of gas is hindered because they
are drawn forward by the movement of the projectile. This uni-
directional gas stream may have a different composition from that
of the rest of the gas, since an exothermic reaction would be pro-
moted by cooling. This possibility may be important with respect
to erosion, because this stream of gas adjacent to the surface of
the bore might react with it.
ИД/ The adiabatic explosion temperature (see Sec, 36) is
independent of the amount of the propellant. The temperature of
the gases at the muzzle, however, is lower the smaller the amount
of charge. For a 3-in, AA gun Ю, the muzzle gas temperature was
calculated to be 1бДо°С for a charge of U.8h lb of pyro powder,
for which the explosion temperature was 2?00°C. With a charge of
5.00 lb of NH powder, which had an explosion temperature of 2Д00°С
the muzzle gas temperature was calculated to be 1Д30°С [Tolch,
1936b, p. Д].
- 79 -
CHAPTER VII. REACTION OF THE TUBE TO FIRING
$1. Temperature of the tube
Direct measurements of the temperature of a gun tube haflre
been made by means of thermocouples welded to its outer surface.
The average results obtained for a number of different guns at
Aberdeen Proving Ground are summarized in Table XIII, which has
been copied from a survey by Lane [1938] . In arriving at this
average rise of temperature per round, allowance was made for
cooling effects when the fire was slow enough to warrant such a
correction. In the case of the 3-in. AA gun Ю, for instance,
the cooling was found to be unimportant at rates of fire of 10
rounds/min and more [Tolch, 1936b]. The larger temperature rise
per round shown in Table XIII for the measurements near the
muzzle compared with those near the breech end of the tube re-
sulted from the heating of a smaller amount of metal rather than
from the presence of a larger quantity of heat. This situation
is demonstrated by the figures in the last column, which show that
the most heat was absorbed by the part of the tube farthest from
the muzzle.
Translation of these results into terms of the heating of a
gun under service conditions is difficult except in the cases Of
very rapid fire or of sustained fire at a steady rate. The ex-
pected temperature rise for a single burst fired very rapidly is
practically the product of the number of rounds fired in one burst
and the average rise in temperature per round. Thus Lane [1935]
calculated that the bore surface of an aircraft machine gun reached
Table Kill. Heating of gun tabes firing single-base powder*
Gun	Projectile and Velocity	Firings	Tube Diam. (in.)	Dist. from Muzzle (in.)	Max. Temp. Measured (°C)	Average Temp. Rise (°C/md)	Average Heat Absorbed (cal/cm2 rnd)
Cal. .30 tank machine gun	172-gm ball 2600 ft/sec	Mean of thou- sands of rounds	1.21 1.21	3.7 11.2	200-400 Maintained	<> • О p 3> i	d «3 OJ CO C\ 1 1 ' " ' | co t L_!
Cal. .50 KoG., heavy barrel air-cooled	750-gm ball 2600 ft/sec	100 md and 2(199) rnd with 15 min cooling between groups	1.5 1.87 2.31 1.9b	5.25 17.1 23.5 27.25	38b 370 314 322	1.36 1.26 .89 1.13	3.3b b,95 5.b5 li. 76
Cal. .50 M.G., water-cooled	750-gm ball 2б00 ft/sec	2(100) rnd and 1(198) rnd	——		100Ь	—	-
75-mm M1897E3	15.96-lb slug 1755 ft/sec	Group of 300 md	b.80 5.28 5.67	12 36 55.5	320 328 328	1.51 l.bo 1.33	b.55	1 5.65	co 6.51i
3-in. AA T8	15-lb slug 2600 ft/sec	Four groups 100 md each	5.03 5.86	12 b8	352 295	3.30 2.39	11.15 12.5b
3-in. AA М3	15-lb slug 2600 ft/sec	Group of 2b7 rnd	5.95 7.28	13 63	b30 360	2.18 1.59	12.0 lb.2
Ю5-ПШ1 AA M1	33-lb slug mod. 2800 ft/sec	Group of 169 md	6.95 8.33 9.69	12 88 16b	285 303 282	2.01 2.06 1.89	9.5 16.2 21.8
*After Lane [1938, Table I].
Corresponding values for double-base powder were 1,1b and l55°C/md and 3.011 and b.25 oal/cm2rnd.
^Temperature of outside barrel practically constant at temperature of boiling water.
-81 -
137O°C after having fired 600 rounds in min. In this calcula-
tion the cooling effect was allowed for to the extent of h. per-
cent of the heat input. In calculating the temperature of the
tube after sustained fire at a steady rate it is necessary to make
allowance for the cooling, which depends materially on the wind
velocity. Cooling rates for the same guns listed in Table XIII
have been- compiled separately by Lane [1939a].
One important way of expressing the heating of the tube is
in terms of the rate of fire necessary to maintain a particular
temperature. For the caliber .30 machine gun these rates, meas-
ured directly for temperatures of 200°, 300° and ЦОО°С,above
ambient temperature, are given in Table XIV in comparison with
similar rates that had been calculated from the results of temper-
ature measurements with other guns. Such data are of practical
importance in deciding on allowable maximum rates of fire; for if
the temperature at the breech end of the tube increases too much,
the steel will be weakened to such an extent that the gun may
burst. Tolch [1936a] calculated for the 10^-mm AA gun M1 that at
16Ц in, from the muzzle the maximum allowable temperature was
йО£°С; that is, at this temperature the tensile strength of the
steel had decreased to such an extent that the factor of safety
was reduced to unity.
Tho effect of artificial cooling of the barrel, as by the use
of a self-circulating water cooler, is illustrated by the data in
Tables XIII and XV for the air-cooled and water-cooled caliber .5>0
machine guns. After similar firing of the same ammunition, the
- 82 -
Table XIV» Temperature of the breech end of the gun tube
as a function of the rate of fire; single-base
povrder.
Temperature Above	Eate of Fire Necessary to Maintain Temperature (rounds/min)				
Ambient C'c '	Cal. .,30lCal. Л0 bi.O. Q. a i r.iv_r>on?r>r'c ......		7/ Ml 897E3C	3-in. AA Gun M3d	105-mm AA Gun Ше
200	1U	8.7	3,3	1.1	0.9
300	17.8	14.3	3.5	1.8	1.4
4oo	22J	20.8	7,7 —_   	2.6	2.0
Corresponding rates of fire obtained with double-bo.se
powder were; 200^C, 9.1;'300cC, 1^.4; 400°C, 18.8 md/min
[Tolch, Ш9 .
bTolch [1936c].
cThis gun had.been modified by the removal of. the bronze
jacket from tho regular gun of this model. It was concluded as
a result of the temperature measurements during firing tests
that ’’the increase in heating effect due to the modification is
partially, if not ’wholly, compensated for by the increase in
cooling rate1’ [Dickinson, 1936] .
^Tolch [1936b 1.
eTolch [1936a].
barrel of the former had reached an average temperature of nearly
ЗбО°С, whereas that of the latter was not much above 100°C. The
quantity of heat absorbed by tho water-cooled barrel was nearly
40 percent greater than that absorbed by the air-cooled one; and
yet its projectile derived 1 percent more energy from the same
amount of powder. Thus the lowered temperature of the barrel,
which tends to increase the life of the barrel, was secured with-
out any loss of efficiency.
i>2. Distribution of energy in gun
The proportion of tho total energy of the powder that is
absorbed by the gun tube is shown in Table XV in comparison with
- 83- -
tho distribution of the remainder of the energy of the powdor.
The amount shown as absorbed by the tube includes that absorbed
by the brass cartridge cases. For the caliber .50 machine guns
this part was found by a calorimetric measurement to amount to
about 300 cal, which raised the temperature of the case to about
81°C. The percentages of energy absorbed by the tube, shown in
Table XV, agree reasonably well with the figure of 22 percent
calculated by Cranz and Rothe [1908] and with that of 15 percent
deduced by Muraour [1925, p. 1x77] from closed-chamber measure-
ments .
Table XV, Percentage distribution of energy of powder,
Distribution	Cal. ,5o М2 Machine Gun		3-in, AA Gun Юс	
	Air-cooled, Pyro Powdera	Water-cooled, Pyro Powder^	Pyro Powder	NH Powder
Velocity and spin of projectile Heat of gun Velocity of gases Heat of gases	28 16 27) > 56 29 J WO	29 22 271 >59 22 J Too	29 11 60 100	32 9 $9
Energy (cal/rnd)	11,31x0	11,31x0	1,035,000	1,51x0,000
aMuzzle velocity, 2600 ft/sec. Fired 5>00 rounds in three
groups at different rates [Tolch, 1936c],
^Muzzle velocity, 2600 ft/sec. Fired 1x00 rounds in three
groups at different rates [Tolch, 19371 .
&Muzzle velocity, 2800 ft/sec. Pyro powder: 15 rounds in
U5 min; NH powder; 25 rounds in 80 min [Tolch, 1936b],
53.	Heat of friction
Transfer of some of the energy of the powder to the tube
takes place indirectly by means of the heat of friction of the
- ВЦ -
projectile as it passes down the bore (see Sec. Ц6) as well as
directly by contact of the hot gases. A measurement of the ex-
tent of this indirect transferwas attempted [Ord. Dept. 192Ц]
by comparison of the heat absorbed by two 37-mm guns that had
been fired 100 rounds each under the same conditions, except
that the projectiles for the one gun had standard bands, where-
as those for the other gun had very narrow bands, the cylindri-
cal portion having been 0.03 in. wide instead of 0.5 in. Each
gun was immersed in the same quantity of water at the end of
firing. The rise in temperature of the water was 5°C in both
cases. Hence, as far as this somewhat rough measurement was
concerned, the heat of friction was probably less than 10 per-
cent of the heat absorbed from the powder gases.
54.	Temperature of the surface of the bore
No direct measurement of the temperature of the surface of
the boro of a gun has been attempted during firing. Some measure
ments have been made directly after firing by pushing a thermo-
couple junction into the muzzle of the gun and holding it against
the bore surface with an asbestos pad. Such a procedure yields
a result of very questionable validity, because of cooling before
the measurement can be made.
The closest approach to a direct measurement of the tempera-
ture of the bore surface was made by Kosting [15351 on a Garand
caliber .30 automatic rifle. A thermocouple junction was placed
at the bottom of a hole drilled into the barrel 7 in. from the
breech end (0.06 in. in front of origin of rifling) so that the
-•85 w
U5/
junction was only 0.077 in- iron the. bore surface. The maximum
temperature after firing £1 rounds in 1.3 min, with the tube
already hot from previous firing, amounted to U85°C. At the same
time the temperature at the surface on the sane radius was b28°C,
Hence the temperature of the bore surface was estimated to be
somewhat in excess of 5>00°G. Measurements at several other points
along the barrel were made simultaneously by means of recording
potentiometers. They indicated that longitudinal heat flow was
much greater than radial heat flew.
The temperature of the bore surface was computed from that
of the outside surface of the tube of a 10^-mm AA gun Ml by Tolch
[1936a, p. 10], using the Fourier equation for heat flow. The
greatest difference between inside and outside temperatures was
at the measuring point nearest to the breech. There the maximum
outside temperature was 279°C, and the corresponding bore tempera-
ture was calculated to be 3h9°C; but this result depends on several
somewhat doubtful assumptions.
The calculation of the temperature to which the bore surface
is raised by a single round is even more uncertain. Lane [1939b]
developed a method suggested by R. H. Kent that is based on a
known rate of heat input. For a 75-mn gun an increase of 179°C
U5/ In a private communication, dated Aug. -22, 19^2,
Kosting pointed out “that because of the use of the recording
potentiometer the time lag would be such as to measure average
temperatures and not peak temperatures, and also that the thermo-
couples placed within the holo drilled into the barrel were held
in place by friction and were not spot-welded to the steel. I
now look with disfavor on any experimental work for evaluating
temperatures in which the thermocouple is not spot-welded at the
point where the temperature is to be measured.1*
- 86 -
was indicated at the interface, whereas it was only 2° at a depth
of 0.0^5 in. below the surface. Kent [19h1] himself criticized
this method, on the grounds that it assumes that the heat capacity
and conductivity of the surface layer of the bore are those of the
steel throughout the tube, whereas he pointed out that possibly
these properties are considerably different in the altered surface
layer. He recommended that an attempt be made to measure them.
55.	Dilation of the bore
Part of the pressure of the powder gases during firing
neutralizes the residual compressional stress that is present in
a modern gun as a result of the method of manufacture (see Sec. 6),
and then the remainder of the pressure places the tube in a state
of tension. There is no quantitative information as to how much
compressive stress is retained by a built-up gun or by a radially
expanded (cold-worked) one. The final machining operations,
especially the rifling, must relieve some of the compressive
stress, and later, when the gun is in service, probably more of
it is gradually dissipated. The calculation of the increase of
diameter of the bore from the pressure is further complicated by
the nonhonogeneity of the stress distribution that is occasioned
w
by the rifling. Justrow [1923] rather naively disregarded these
Ц6/ Dr. P. R. Kosting (private communication, Aug. 22, 19h.2)
remarks that recent British firings have shown that the engraved
portions of the rotating bands of some recovered projectiles were
larger than the diameter of the bore of the gun. Hence the tube
must have expanded ahead of the rotating band; and therefore the
stress distribution in the tube is more complicated than if the
gun is considered merely as a cylinder subject to a uniform inter-
nal pressure.
- 8? -
factors in his elaborate calculations of the dilation of the bore.
The bore diameter is also changed by the rise of temperature.
If the whole tube heats up gradually, the inside diameter increases.
Thus for a 105-mm gun the increase would amount to about O.OOli in.
for each 100°C rise of temperature above ambient [Tolch, 1936a,
p. 6] .
56.	Contraction of the bore
Contraction of the bore may occur whenever the bore layers
are stressed beyond their yield point, which varies inversely as
some function of the temperature. A sudden increase of 100°C in
the temperature of the bore would correspond to an increase of
2	4?/
30,000 lb/in, in the compressional stress, Fleming [1918] as-
cribed to this cause the complete elimination of the rifling in
a Lewis antiaircraft machine gun that had been fired 2500 rounds
automatically (cyclic rate not known), during which time the barrel
had been observed to have become red hot. He suggested that the
projectile acted as a mandrel in the contracted bore.
57• Elongation of the tube
Compressive stress in the inner layers of the tube may be re-
lieved by elongation of the tube. This action is assisted by the
longitudinal stress caused by friction between the projectile and
the bore. Liners have been known to be caused to protrude in this
manner, and even 15-in. gun tubes have been reported [Miller, 1920,
p. 53] to have been permanently elongated as much as J-in.
Ц7/ R* W. Goranson, private communication.
- 88 -
58. Tangential stress
The rotary motion of the projectile during firing imposes a
considerable tangential stress on the tube. For а 2Ц0-тт howitzer
this stress was calculated under various assumptions to be as high
as 9000 lb/in^ It was therefore considered to have been a factor
that contributed to the failure of a number of such guns by burst-
ing or swelling [Ord. Dept., 1931]. Justrow [1923] attributed to
the tangential stress on the sides of the lands considerable in-
fluence as a cause of erosion.
- 89 -
BIBLIOGRAPHY AND AUTHOR INDExkl/
for PART ONE
A. C. [19U2c] (Sec. 18)
’’Deformation of driving bands on 3-in. proof shot/’ Adv, Council
Sci. Res. Tech. Dev. to British Ministry of Supply, A. C. 2000
(Apr. 28, 19h2).
Bender, V. E. and J. N. Pappas [19k1 ] (Sec. 15)
’’Investigation of steel compositions for centrifugal castings
that can be heat-treated to a yield strength of 121,000 to
135,000 lb/in.8," Watertown Arsenal Re pt. No. 3lh/U2 (July 22,
191+1), 6 p.
Bennett, Albert A. [1921] (Sec. 30, h3)
’’Tables for interior ballistics,’’ Office of the Chief of Ord-
nance, Washington, D.C. (Apr. 1921).
Bone, W. A. and D. T. A. Townsend [1927] (Sec. Ц0)
Flame and combustion in gases, Londons Longmans, Green (1927)t
------------------------------
Boys, S. F. and J. Corner [ 19li1 ] (Sep. 30)
’’Structure of reaction zone in burning of a colloidal propel-
lant,’’ Adv. Council Sci. Res. Tech. Dev. to British Ministry
of Supply, A. C. 1139 (Aug. 22, 19Ш).
Brinkman, H, [19Ц0] (Sec. 36)
["Measurement of high temperatures of gases by the emission
spectra"], Nederland. Tijdschr. Natuurkunde 7, 65-85 (191|O);
Ch. Abs. 3h, 7670.
Bruin, G. de [1930]
"La poudre sans fumee et I1erosion des bouches a feu. I. Court
aper<£u historique et critique du sujet," Communique de la Ste.
Anme. "Fabrique Neerlandaises d’Explosifs" No. 10 (1930), 39 P*
English tr. by Lt. Col. Aiken Simons, Mil. Sales Div., E. I. du
Pont de Nemours and Co. (Mar. 1931), h9 p.; Ord. Dept. Lib,
Bruin, G. de and P. F. de Pauw [1928] (Sec. 32, 33, Ц0)
"La temperature de combustion de la poudre sans fumee en fonction
de sa composition chimique. II. Partie experimentale’’ [See
Moesveld, 1928, for Part I»], Communique de la Ste. Anme.
4’Fabrique Neerlandaises d’Explosifs" No. 8 (1928); Ord. Dept. Lib,
Ц7/ The section number given on the same line as the author’s
name refers to the present report.
- 90 -
Bruin. G. de and P. F. de Pauw [1 929] (Sec. 32, 33)
"La temperature de combustion de la poudre sans fumec en fonction
de sa composition chimique. III.,11 Communique de la Ste. Anme.
"Fabrique Neerlandaises d’Explosifs" No. 9 (1929); Ord. Dept. Lib.
Bruin, G. de and P. F. de Pauw [1931] (Sec. 13)
"La poudre sans fumee et 1*erosion des bouches a feu. II* Partie
experimentale," Communique de la Ste* Anme. "Fabrique Neerlan-
daises d’Explosifs" No. 11 (1931), 27 p. English tr. by M. S. P.,
Mil. Intell. Div., War Dept.; Ordnance Dept. Library.
Bur. Stand. [192Ца] (Sec. Ц6)
"A digest of ballistic data on large naval guns obtained for
the Bureau of Ordnance, Navy Department by the Bureau of Stand-
ards," Washington, D.C. (Oct. 192Ц).
Bur lew, J. S. [19h-2] (Sec. 7)
A brief history of tapered bore guns, NDRC Report A-h3 (OSRD
No. 5l5) (Apr. 15, 19U2).
Burlot, E. [192Ц] (Sec. 37)
"Note relative a la determination experimentale de la force et
du covolume des explosifs," Mem. poudres 21, Ц11-90 (192Ц).
Carl, Leroy R. [19h-0] (Sec. 22)
"The breaking theory of detonation," J, Franklin Inst. 230,
75-9h, 207-227, 355-37U (19Ц0).
Charbonnier, P. [1908] (Sec. 13)
Balistique Intdrieure, Paris; Doin (1908).
Charbonnier, P. [1922] (Sec. 13)
"La veine gazeuse," Men. artillerie franqaise 1, 1001-11 (1922).
Cranz, C. and R. Rothe [1908] (Sec. 52)
"Temperatur und Warme Messungen am Infanterie gewehr M98S,"
Z. ges. Schiess u. Sprengstoffw. 3, 301-5, 327“32 (1908).
Cranz, C. and H. Schardin [1932j (Sec. Ц6)
"Eine neue Methode zur Messung des Geschosswiderstandes in
Rohr," Z. tech. Physik 13, 12Ц (1932). Reprint translation
in Ordnance Dept. Library.
Crawford, D. J., Jr. [1937] (Sec. 30, Ц2)
"The applicability of photography and spectroscopy to some
problems in interior ballistics," Watertown Arsenal Rept.
No. 122/9 (1937), 13 p. and bibliography of 5 p.
- 91 -
Crocker, J. A. and N. M. Smith, Jr. [19U2] (Sec. Ц6)
"Bore-frictipn gages,11 Memo, to H. H. Porter OSRD/Sec. t/TR
1107 (Mayli-, 19й2), 3 p.	,	
Crow, A. D. and W. E. Grimshaw [1931a] (Sec. 32, 38)
’•On the equations of state of propellant gas os,” Trans. Roy.
Soc. (London) A23O/;39-r?3 (1931)^
Crow, A. D. and W. E. Grimshaw [1931b] (Sec. 29, 30, 33» 37, hl)
’•The combustion of colloidal propellants,” Trans. Roy. Soc.
(London) A230, 387-h.il (1931).
David, W. T. and-A. S. Leah [193h] (Sec. hi)
’•Specific heat of gases at high temperatures,” Phil. Mag. 18,
307-21 (193h).
de Bruin, G. See; Bruin, G. de
de Marre, Jacob.- See: Marre, Jacob de
de Pauw,. P. F. See;. Bruin, G. de and P. F. de Pauw
Dickinson, W. D. [1 936] (Sec. 51)
"Study of the heating and cooling df the bore of the 75-ram
gun M189733,“Aberdeen P. G., Ballistic Res. Lab. Rept.
No. Ц9 (Apr. 22, 1936), 6 p.
Donald, W. G. [1937] (Sec. 15)
’•Investigation of high-strength steel compositions,” Water-?
tow Arsenal Rept. No. 31Ц/2О (May 12, 1937), 7 p.
Dunkle. Sec also: Volsk and Dunkle
Dunkle, 0. G. [1935] (Sec. 32, 33, 3h)
"Calorific values of smokeless powders as affected by varia-
tions in composition, granulation, etc.,” Picatinny Arsenal
Tech. Rept. No. 620 (Apr. 23, 1935), 13 p.
Dunkle, G. and N. T. Volsk [1932] (Sec. 311)
"Calorific values of smokeless powders as affected by variations
in composition, granulation, etc.,” Picatinny Arsenal Tech.
Rept. No. 231 (June’ 7, -1932), 7 p.
Fleming,. J. .Р,-  [-1918] .(Sec. 56)
"Erosion tests of high silicon-chrome-vanadium steel in Lewis,
aircraft automatic rifle barrels,” manuscript, Ordnance Dept.
Library (June 1918).
- 92 -
Gerlich, H. [1930] (Sec., 3)
"Increased bullet speeds. Effects and possibilities of a
German rifle and its ammunition,'1 Army Ordnance 1Q, -398-RDh
(1930). (Reprinted in American Rifleman, Sept. 193G.)
Gerlich, H. [1931] (Sec. 3)	•
4An advanced era of bullet velocities. The attainment of
high speeds and their effects on armor,11 Army Ordnance 12.,
wo-юз (1931).	; .. .
Gerlich, H. [1933] (Sec. 3)
"The ballistic efficiency of guns.. A great increase of
velocity has been attained," Army Ordnance 13,215-9 (1933)*
Greaves, R.. H., H. H. Abram and S. H, Rees [1 929] (Sec. 4?)
"Erosion of guns," J. Iron and Steel Inst. 109,.’113-16?
(1929). Includes bibliography of Ц p.
Hayes, T. J., editor [1938] (Sec. 3, 5, 17, 32, Ц3)
Elements of ordnance; A textbook for use of cadets of' the
ULS?' Military Academy, New York: Wiley (1938), 715 p.
Henderson, J. B. and H. P. Hasse [1922] (Sec. Ц1, Ц9)
 "A contribution to the thermodynamical, theory of explosions,"
Proc. Roy. Soc. (London) A100, Ц61-82 (1922); Mem. artillerie
frangaise 2, 1078-1101 (1922J.
Hirschfelder, J. 0., F. T.. McClure ahd 0. F. Curtiss [19Ц2]
(Sec. Ul]
Thermochemistry and the equation of state of propellant
gases, M)RC Rept. A-h8 G5SrD~~No] 5U7) (Apr- 8, 19h2).
Howe, Henry M. [1918] (Sec. 9)	.	•
"The erosion of guns," Trans. Am. Inst. Min. Met. Engrs.
58, 513-96 (1918).
Hugoniot and Sebert [1882] (Sec. 13)
"Etudes des offets de la poudre dans un canon de 10 cm,"
Mem. artillerie marine 10 (1882).
Justrow, Capt. [1923] (Sec. 9, 19, I4.6, 58)
"Theoretical consideration concerning the life of the tubes
of our guns, trench mortars, rifles and pistols and their
relation to the behavior of projectiles," "Heerstechnik,"
(Jan. 1923), translation, Ordnance Dept. Library.
- 93 -
Kast, H. [19Ю] (Sec. 39)
["The determination of explosion temperature’1], Z. ges, Schiess.
u. Sprengstoffw. 5, 205-8, 248-54 (1910); Ch. Abs. 4, 2877.
Kent, R. H. [1933] (Sec. 3)
’'Times of flight of a Gerlich 3-in. antiaircraft gun/’ first
addendum and Appendix C of "First and final report of test of
Halger-Ultra rifle designed by H, Gerlich," 29th partial Rapt,
of Ordnance Program 4975 and 2nd partial Rept. of Ordnance
Program £019, Aberdeen P. G. (Jan. 1933).
Kent, R. H. [1935] (Sec. 30)
"The influence of radiation on the ignition and burning of
powders," Aberdeen P. G., Ballistic Res. Lab. Rept. No. 9
(1935), 7 P.
Kent, R. H. [1938a] (Sec. 39, 41)
"The flight of the projectile," J. Franklin Inst. 226, 19-33
(1938).	“
Kent, R. H. [19U1] (Sec. 54)
Remarks at conference on gun erosion, Watertown Arsenal,
Watertown, Mass. (Oct. 15, 1941). Report of conference,
Watertown Arsenal, p. 15.
Kent, R. H. and H. P. Hitchcock [1929] (Sec. 48)
"Interior ballistic firings in the 240-min howitzer No. 292 on
free recoil carriage," 4th partial Rept. of Ordnance Program
4259 (Sept. 19, 1929).
Kent, R. H. and J. R. Lane [ 194-1 ] (Sec, 41, 42)
Remarks at conference on gun eirosion, Watertown arsenal,
Watertown, Mass. (Oct. 15, 1941).  Report of conference,
Y/atertown Arsenal, p. 33.
Kosting, P. R. [1935] (Sec. 54)
"Investigations of the cause of bore enlargement in the Garand
caliber .30 semiautomatic rifle No. 49," Watertown Arsenal
Rept. No. 739/3D (June 6, 1935).
Kosting, P. R. [1939] (Sec. 19)
"A metallographic and diffraction study of erosion of guns,"
manuscript, Ordnance Dept. Library, 3 p.
Kutterer, R. E. [1942] (Sec. 46)
"The measurement of shot resistance in the bore of a gun,"
Adv. Council Sci. Res. Tech. Dev. to British Ministry of
Supply, л. C. 2244 (July 11, 1942). Extended abstract of
- 9h -
articles in. Wehrtechnische Monatshefte 39, h96, $36 (1935)
and in Меи. artillorio francaise 15 (193^).
Lane, J. R. [1933] (Sec. 9, 19)
Memorandum report on test of six 3-in. antiaircraft guns,
Ml 925 — radially expanded, Ordnance Program R6l5 (Apr. 21|,
1933), 6p.
Lane, J. R. [1935] (Sec. 51)
’’Temperature of an aircraft machine-gun barrel when fired at
a rate of 1200 rnd/min,” Aberdeen P. G., Ballistic Res. Lab.
Rept. No. 23 (Nov. 1, 1935), 6 p.
Lane, J. R. [1938] (Sec. 51)
’’Heating of guns,” Aberdeen P. G., Ballistic Res. Lab. Rept.
No. 10U (May 20, 1938), 12 p.
Lane, J. R. [1939a] (Sec. 51)
’’The cooling of guns,” Aberdeen P. G., Ballistic Res; Lab.
Rept. No. 1Ц6 (Apr. 26, 1939), 15 p.
Lane, J. R. [1939b] (Sec. 5й)
"Temperature of 75~mm cartridge case," Aberdeen P. G.,
Ballistic Res. Lab. Rept. No. 159 (Sept. 27, 1939), 8 p.
Lennard-Jones, J. E. and J. Corner [19Ц1] (Sec. 30)
"Burning of propellant and effect of gas flow over its sur-
face," Adv. Council Sci. Res. Tech. Bev. to British Ministry
of Supply, A. C. 1173 (Sept. 5, 191+1).
Lewis, Bernard and G. von Elbe [1938] (Sec. 36, hl, h2)
Combustion, flames and, expl isions of gases, Cambridge Univ.
Press (193Ю, Ul5 p.
Littler, W. B. [19U2] (Sec. 26)
'•Summary of propellants in use in British service,” Adv.
Council Sci. Res. Tech. Bov, to British Ministry of Sunply,
A. C. 1802 (Mar. 7, 19U2).
Macnab/U, and E. Ristori [189h] (Sec. 3h)
"Researches on modern explosives,” Proc. Roy. Soc. (London)
56, 8-19 (189U).
Macnab, W. and E. Ristori [1900] (Sec. 36)
"Researches on modern explosives; second communication,"
Proc. Roy. Soc. (London) 66, 221-32 (1900).
- уз -
Mallard., Е. and Н. Le Chatelier [1883] (Sec. 38)
Constants for equations for temperature," Ann. Mines Ц, 379
(1883).
Marre, Jacob de [1886] (Sec. 2)
'‘Perforation des tiles et plaques de fer et d’acier en tir
normal/1 Mem. artillerie francaise 1h (1886).
Marshall, Arthur [191 7] (Sec. 25, 26)
Explosives, London: Churchill; Philadelphia: Blakiston (ed. 2,
1917) , vol. I and II, 795 p., vol. Ill, 286 p.
Miller, H. W. . [1920] (Sec. 18, 57)
"Preliminary report on character, cause, rate and effect of the
various phenomena of the wear and erosion of guns,1’ manuscript,
Ordnance Dept. Library (1920), 180 p.
Moesveld, A. L. Th. [1928] (Sec. Ц2)
'’La temperature de combustion de la poudre sans fumee en fonc-
tion de sa composition chimique. I. Partie theorique" [See de
Bruin and de Pauw, 1928, fir Part II.], Communique de la Ste.
Anme, "Fabrique Neerlandaises d’Explosifs1’ No. 7 (1928).
Muraour, H, [1919a] (Sec. 39)
['’Determination of the temperature reached in explosive
reactions'1], Gomptes Rendus 168, 995-7 (1919); Ch. Abs. 13,
1766.
Muraour, H. [1919b] (Sec. hO)	,
["Comparison of temperatures of explosion calculated from
specific heats with those calculated from explosion pressures1’],
Comptes Rendus 169, 723-6 (1919); Ch. Abs. 1U, 631.
Muranir, H. [1923] (Sec. 37)
"Note sur 1*influence du refroidissement dans la mesure des
pressions explosives," Mem. poudres 20, 323~3h (1923), tr.
by Major Aiken Simons, .Ordnance Dept. Library.
Muraour, H. [192Ца] (Sec, ЦО, Ц2 )
"Notes sur la theorie des explisifs," Mem. artillerie francaise
3, 329-338 (192Ц).	&
Muraour, H. [192ЦЬ] (Sec. Ц0)
"Comparison entre les temperatures d’explosions calculees a
partir des pressions explosives et les temperatures d’explo-
sions calculees a partir des chaleur specifiques," Mem.
artillerie francaise 3, 3h9-63 (192Ц),
- 96 -
Muraour, JI. [192Цс] (Sec. ЦО)
"Note sur la chaleur specifique des’gaz h haute temperature.
(Comparison des experiences de Berthelot et’Vieille avec les
experiences effectuoes au Laboratoire de Nerhst)," Mem. ar-
tillerie fraricaise 3, 373-80 (192Ц).
Muraour, H. [1925] (Sec. 37j 52)
"Notes de balistique interieure. II. Sur 1*influence du
refroidissement dans la mesure des pressions explosives.
III. Sur ,1a perte par le refroidissement dans le tir au
canon," Mem. artillerie francaise'4, Цб0-7Ь, Ц75-8-(-1925).
Muraour, H. [1926] (Sec. Ц0)
["?i comparison between explosion temperatures calculated from
the specific heats and those calculated from-the explosion
temperatures"], Bull. Soc. chim. 39, 389-96 (1926); Gh. Abs.
20, 2Ц13.	.
Muraour, H. [1931 ] (Sec. 30) '
"Sur une theorie de la combustion, en vas clqs> des poudres
colloidales," Comptes Rendus 192, 227-9. (1931).
Muraour, H. and G. Aunjs [1938] (Sec. 29)
"Verification de la loi de combustion par couches paralleles
des poudre colloidales," Comptes Rendus 206, 1723-6 (1938).
Naval Ordnance [1936] (Sec. 15)
"Specifications for gun forgings for the United States Army
and Navy," Naval:Ordnance Pamphlet No. 9, WashingtonJ Govern-
ment •Printing Office (5th rev., May 1936). ...'
Naval Ordnance [1939] (Sec. 3,	Ю, 12; 15, 23, U3)
Naval ordnance* a textbook prepared for the use of midshipmen
at the' U.'S. Naval Academy, by,Officers of the U.S. Navy,
Annapolis: U.-S. .Naval Institute (1939), Ц81 p.
Noble, Л. [189Ц] (Sec. 3U)
"On methods that have, been adopted for measuring pressures
in the bore of guns," Oxford: British Assoc, (ij&9U); reprinted
in Noble (1906 reprint], pp. Ц82-98.
Noble, A. [1905] (Sec. 32, 3h, 3?)
4Researches on explosives, III," Trans. Roy. Soc. (London). ‘
205л> 201-36 (1905).
Noble, A, [1906] (Sec. 32, 3U, 35,. hO)
"Researches on explosives',. IV," Trans. Roy. Socv (Londun)'
206A, L53 (1906).	,'
- 97
Noble, л. [1906 reprint] (Sec. 36)
Artillery and explosives; essays and lectures written and
delivered at various times, New York: Dutton (1906), 5118 p«
Noble A. and F. Abel [187$] (Sec. 33, 36, 37, 118)
’’Researches on explosives, I,” Trans. Roy. Soc. (London)
(1875); reprinted in Noble [1906 reprint], pp. 99-230.
°- в* p- [19M] (Sec. 3)
Ordnance Board (Great Britain), Proceedings No. 11379 (Mar. 13,
19111), ”High-velocity guns on the Gerlich and sm jothbore
principles.11
Crd. Dept. [1922a] (Sec. Ц.6)
’’Report of 21i0-mm howitzer tests. Firing record No. 191$,
referred to in memorandum dated Nov. 28, 1922 by A. Adelman,”
Technical Staff Test Program 1922-101.
Ord. Dept. [1922b] (Sec. Ц6)
’’Report of experimental determination of the frictional resis-
tance offered by the rotating bands of projectiles vriien passing
through 75-mm guns,” Technical Staff Test Program 1922-108.
Ord. Dept. [1921;] (Sec. 53)
’’Heating of rifle barrel due to friction of rotating bands,”
first progress report of Ordnance Program 111179 (Apr. 9, 1921г).
Ord. Dept. [1931] (Sec. 58)
’’Report of investigation of 2Ц.0-ПШ1 howitzers 111918 and M1918A1.
Investigation of causes of bursting of howitzer No. 5 (Dec. 3,
1931); TSTP 1932-657.
Ord. Dept. [19110a] (Sec. 6)
’’Ordnance Materiel — General,” Aberdeen P. G., the Ordnance
School (Vol. I, Apr. 19Ц0; Vol. II, May 19Ц0).
Ord. Dept. [ 19110b] (Sec. 15)
’’Notes on the selection and use of metals in ordnance design,”
p. 86; Ordnance Document No. 2050 (May 19110).
Pike, H. H. H. [19112] (Sec. 27, 32)
’’Thermochemical data for the products of propellant explosions,”
Adv. Council Sci. Res... Tech. Dev. to British Ministry of Supply,
a. C. 1862 (Mar. 20, 19112).
Piobert, G.	[ 1839] (Sec. 29)
Traite d’Artillcris, Proprieties et Sffets de la Poudre (1839).
.  - 98 -
Poppenberg, 0. [1909] (Sec. ho)
[’’Calculating the temperature of explosion ..in explosives”],
Z. ges. Schiess u. Sprengstoffw. 4, 36 7 (T9O9); Ch. Abs. 4,
16?U
Poppenberg, 0. [1923] (Sec. 39, hl)
"Uber die Zersetzung von Explosivetoffen,” Z. angew. Chen.
36, 80-8$ (1923); Ch. Abs. 17, 2361i.
Poppenberg, 0. [1924]
”Sur la decomposition des substances explosives,” Men. 
artillerie francaise 3, 383-402 (1924). (Tr. of Poppenberg,0.
[1923].)
Poppenberg, 0. and E. Stephan [1909a] (Sec. 39)
["Decomposition, heat of combustion and temperature of explosion
of explosives”], Z. ges. Schiess u. Sprengstoffw. 4, 281-303
(1909); Ch. Abs. 4, 1675-
Poppenberg, 0. and E. Stephan [1909b] (Sec. 35)
["Decomposition of povjders in guns during firing”], Z. ges.
Schiess u. Sprengstoffw. 4, 388 (1909); Ch.- Abs. 4, 1674.
Poppenberg, 0. and E. Stephan [1910a] (Sec. 39)
["The decomposition of explosives”], Z. ges. Schiess u. Spreng-
stoffw. 5, 266-91 (1910); Ch. Abs. 4, 3139.
Poppenberg, 0. and E. Stephan [1910b]	(Sec, 39)
("The decomposition of explosives”], Z. ges. Schiess u. Spreng-
stoffw. 5, 452, 474 (1910); Ch. Abs. 5, 1$15.
Sarrau, E. [1893] (Sec. 37)
Introduction a la theorie des explosifs, Paris (1893).
Sarrau, E. and P. Vieille [1884] (Sec. 34)
Mem. poudres et salpetres 2, 126, 337 (1884-5).
Schmidt, Albert [1 929] (Sec. 40)
"Beitrage zur thermodynamischen Behandlung oxplosibler Vorgange,”
Z. ges. Schiess u. Sprengstoffw., parts I and.II;.24, 41-46,
90-93 (1929); part III, 25, 97-101, 144-48 (1930),“"
Schmidt, Albert [1934] (Sec. 32)
"Therraochenische Tabellen fur die Explosivchemie,” Z. ges.'
Schiess u. Sprengstoffw. 29, 2$9-66, 296-301 (1934),
- 99 -
Siwy, P. [1906] (Sec. 35)	’ '
'‘Die Abnutzung der C-eschtltze und deren Ursachen," 2. ges.
Schiess u. Sprengstoffw. 3, h2., 66 (1908); Ch. Abs. 2, 2862.
Smith, N. M., Jr. [19h2] (Sec. U6)
The piezoelectric projectile accelerometer and a bore-
friction gage, NDRC Rept. A-59 (OSRD No. 808) (Aug. 7, 19Ц2).
Storm, C. G. [1925] (Sec. 25)
"’The development of flashless, nonhygroscopic powders,1’
manuscript, Ordnance Dept. Library (Feb. 18, 1925), 16 p.
Tolch, N. A. [1935] (Sec. 51)
’’The rate of erosion of the Browning caliber .30 tank type
machine gun Ml 919 as dependent on the temperature of the
gun and other factors,11 Aberdeen P. G., Ballistic Res. Lab.
Rept. No. 13; 21 p. and graphs.
Tolch, N. A. [1936a] (Sec. 51. 5h, 55)
"On heating effects and endurance properties of the 105-ram
antiaircraft gun Ml as determined by rapid-fire tests,11
Aberdeen P. G., Ballistic Re's. Lab. Rept. No. 35 (Feb. 12,
1936), 16 p.
Tolch, N. A. [1936b] (Sec. 50, 51, 52)
"On heating effects and endurance properties of the 3_in.
antiaircraft gun IQ as determined by rapid-fire tests,"
Aberdeen P. G., Ballistic Res. Lab. Rept. No, 39 (Mar. 2,
1936), 19 p.
Tolch, N. a. [1936c] (Sec. '51, 52)
"Heating effects and distribution of the energy of the charge
of the caliber .50 М2 machine gun, heavy barrel," Aberdeen
P. G., Ballistic Res. Lab. Rept. No. 61 (Oct. 1, 1936), 15 p.
Tolch, N.,A. [1937] (Sec. 52)
"Heating effects and distribution of the energy of the charge
of the caliber .50 М2 machine gun, water-cooled type," Aber-
deen P. G., Ballistic Res.’ Lab. Rept. No, 7U (Apr. 5, 1937),
13 ръ
Tulloch, T. G. [1921] (Sec. 13, 19)
Vear in big guns, Woolwichs Royal Artillery Institution
Printing House (1921, written in 191?), 10 p.
Valente, F. A. [1929] (Sec. 3h)
"Calorific values of smokeless powder as affected by variations
in composition, granulation, ignition, etc.," Picatinny Arsenal
Rept. No. R72 (May 15, 1929).
- 100 -
Veblen, 0., and P. L. Alger [1919] (Sec. 18)
"Rotating bands,’1 J. U. S. Artillery 355-390 (1919).
Volsk, N. T. and C. G. Dunkle [1932] (Sec. 3U)
"Study of relation between volatile solvent content and
calorific value of.FNH powders," Picatinny Arsenal Rept.
No. 20$ (Apr. 20, 1932).
Weaver, Warren [19Ц2] (Sec. 3)
"The way nuzzle velocity affects the probability of hitting
aircraft by AA fire," NDRC Memo, Section D-2 (Fire Control)
(Apr. 1, I9h2), 5 p.
NATIONAL DEFENSE RESEARCH COMMITTEE
REPORT NO. A-91 : PROGRESS REPORT
THE EROSION OF GUNS
Part Two: The Characteristics of Gun Erosion
by
John S. Burlew
NATIONAL DEFENSE RESEARCH COMMITTEE
REPORT NO. A-91 : PROGRESS REPORT
THE EROSION OF GUNS
Part Two: The Characteristics of Gun Erosion
by
John S. Burlew
Approved on October 31, 19ц 2
for submission to the Section Chairman
John S. Burlew, Consultant
Section A, Division A
Approved on October 31, 19b2
for submission to the Division Chairman
Approved on November 2,1 9Ц2
for submission to the Committee
L. H. Adams, Chairman
Section A, Division A
Richard C. Tolman, Chairman
Division A
Preface
The work described in this report is pertinent to the project
designated by the War Department Liaison Officer as OD-f>2, to the
project designated by the Navy Department Liaison Officer as NO-23
and to Division A projects PA-230 and РА-2ЦО. Part of the work of
preparation of this report was performed under Contract OEMsr-f>1
with the Carnegie Institution of Washington.
This report has been issued in two volumes. The present volume
comprises Part Two., on the characteristics of gun erosion. The pre-
ceding volume was issued as NDRC Report A-9Q.(OSRD No. 882) and com-
prised Part One, on the fundamentals of ordnance relating to gun
erosion. The '’Bibliography and Author Index" on page 2I4.3 of the
present volume pertains only to Part Two, but the "Subject Index" on
page 2^9 pertains to both parts of the report.
Distribution of copies of the report. — The editorial staff of
Division A completed preparation of this report for duplication on
November Ц; 19u2.The initial distribution of copies was as
follows:
Copies No. 1 to 2Ц, inclusive, to the Office of the Secretary
of the Committee for distribution in the usual manner;
Copies No. 25 to 33> inclusive to the Chief of Ordnance, War
Department (Attentions Col. W. R. Gearhardt, Col. S. B. Ritchie,
Col. R. R. Studler (2 copies), Lt. Col. D. J. Martin, Capt. С. E.
Balleisen, S. Feltman, P. M. Netzer, Technical Library);
Copies No. 3U to 36, inclusive, to Aberdeen Proving Ground
(Attention: Lt. Col. L. E. Simon, R. H. Kent, J. R. Lane);
Copies No. 37 to Ц0, inclusive, to Watertown Arsenal (Attention:
Col. H. H. Zornig (2 copies), P. R. Kosting, H. H. Lester);
Copy No. I4/I to Watervliet Arsenal (Attention: Lt. Col. S. L.
Conner);
Copy No. Ц2 to Frankford Arsenal (Attention: Lt. Col. L. S.
Fletcher);
Copy No. ЦЗ to Springfield Armory (Attention: Capt. A. E,
Benson);
Copies No. ЦЦ to I46, inclusive to the Chief of the Bureau of
Ordnance, Navy Department (Attention: Capt. G. L. Schuyler, Lt. B. D.
Mills, С. B. Green);
Copy Цр. h7 to the Office of the Coordinator of Research, Navy
Department (Attention: Lt. T. C. Wilson);
Preceding Page15 Blank
iii
Copy No. Ц8 to the Naval Research Laboratory (Attention:
R. Gunn);
Copy No. Ц? to the Inspector of Ordnance in charge, Naval
Proving Ground, Dahlgren, Va.;
Copy No.-£0 to С. C. Lauritsen, Vice Chairman, Division A;
Copies No, 51 to 60, inclusive, to L. H. Adams, Chairman,
Section A, Division A;
Copy No. 61 to H. B. Allen, Vice Chairman, Section A,
Division A;
Copy No. 62 to L. J. Briggs, Member, Section A, Division A;
Copies No. 63 and 6J4 to E. L. Rose, Member, Section A,
Division A;
Copy No. 65 to E. R. Weidlein, Member, Section A, Division A;
* Copy No. 66 to J.- S. Burlew, Consultant, Section A, Division
A;
Copy No. 6? to H. L. Curtis, Consultant, Section A, Division
A 5
Copy No. 68 to R; E. Gibson, Consultant, Section A, Division
A; Vice Chairman, Section H, Division A;
Copy No. 6? to W. F. Jackson, Consultant, Section A, Divi-
sion A;
Copy No. 70 to J. F. Kincaid, Consilltant, Section A, Divi-
sion A;
Copy No. 71 to T. C. Poulter, Consultant, Section A, Divi-
sion A;
Copy No. 72 to J. Wulff, Consultant, Section A, Division A;
Copy No. 73 to J. 0. Hirschfelder, Consultant, Section A,
Division A;
Copy No. 7U tO'P. W. Bridgman, Consultant, Section B,
Division, A;
Copy No., 75 to G. B. Kistiakowsky, Chairman, Section B-1,
Division B;
Copies No. 76 to 80, inclusive, to the Secretary of the Com-
mittee for transmittal to L. C. Pauling, Clyde Williams, J. C. W.
Frazer,'I.'If. Stein, J. P. Magbs;
Copy No. 8l to M. A. Tuve, Chairman, Section T, Office of
Scientific Research and Development;
Copy fob. 82 to Lt. Col. K. Maertens, Secretary to Joint Com-
mittee on New Weapons and Equipment;
Copy No. 83 to the Bureau of Ordnance (Attentions Lt. H. W.
Drake);
Copy No. 8Ц to Frankford Arsenal (Attention: The Librarian);
Copy No. 85 to the Chief of Ordnance, Firing Records, Tech-
nical Division (Attention: Mrs. E. T. Ryan).
iv
TABLE OF CONTENTS
PART ONE*
FUNDAMENTALS OF ORDNANCE RELATING TO GUN EROSION
Page
Foreword by L. H. Adams ....................................   ix
Chapter
I.	Introduction .........................................  1
II.	Guns ..........................................         7
III.	Projectiles .........................................   26
IV.	Propellants ........................................   33
.	V.	Burning of the Powder ............................. Ц2
VI.	Movement of the	Projectile	in'the Bore .............   6?
VII.	Reaction of the	Tube to	Firing ..................... 79
Bibliography and Author Index for Part One ..................  89
PART TNG
THE CHARACTERISTICS OF GUN EROSION
VIII.	Magnitude of Erosion ..............................   101
IX.	The Eroded Surface .................................  119
X.	Experimental Methods of Study of Gun Erosion ......	1J?2
XI.	Relation Between Properties of the Gun Metal and
Erosion................................................... 168
XII.	Conditions of Firing that Influence the Rate of
Erosion........................................... 192
XIII.	Effect on Erosion of Leakage of Gas Past the
Projectile................................................   209
XIV.	Life of Guns ...................   .................  2Г9
XV.	Theories of the Mechanism of Erosion...........	235
Bibliography and Author Index for Part Two................... 2^3
Subject Index to Parts One and Two  ......................... 2^9
Supplementary Index of Guns, by Caliber.....................  267
z<Part One appears in a previous volume which is designated as
NDRC Report A-90 (OSRD No. 882).
v
List of Tables
Table	/-	Page
I.	Principal dimensions and other details of repre-
sentative guns and their projectiles .................... 8
II.	Compositions	of	steels	used	in	Navy guns .......... 20
III.	Compositions	of	steels	used	in	Army guns .......... 22
IV.	Compositions	of	steels	used	in	small arms	barrels .23
V.	Approximate proportions of artillery projectiles ..	27
VI.	Nominal compositions of smokeless powders .......... 38
VII.	Heat of explosion,, heat of combustion and tempera-
ture of explosion df propellent powders .................. 18
VIII.	Products of combustion of gunpowder..........,.....  19
IX.	Products of combustion of smokeless powders ........ 50
X,- Variation in composition of powder gases with
change of density of loading ..................... 52
XI. Products of combustion of cordite in a gun com-
pared with those obtained in a closed chamber .... 55
.. XII. Partial pressures of the constituents of powder
gases, and temperature of explosion......................... 66
XIII.	. Heating of gun tubes firing single-base powder .... 80
XIV.	Temperature of the breech end of the gun tube as a
function of the rate of fire; single-base powder., 82
XV.	Distribution of energy of powder ..................  83
XVI.	 Erosion of 155-mm guns .......................    108
XVII.	Comparison of average erosion per round for guns
of different caliber; velocity, 2500 to
2750 ft/sec .............................................. 109
XVIII.	Average thickness of the four parts of the
altered layer 'at the origin of rifling in
37~mm gun No. СЦ6С.......................................   131
XIX.	Hardness of altered layer at surface of bore of
12-in. gun specimens ...............................      138
vi
Table	Page
XX.	The microstructural constituents of steel .......... 1Ц2
XXI.	Cost of ammunition needed for firing guns to
destruction ............................................. 155
XXII.	Properties of special steels tested for drowning
machine-gun barrels ...................................... 170
XXIII.	Firing tests of Browning machine-gun barrels made
of special steels ....................................... 173
XXIV.	Erosion of pure metals as a function of melting
point .................................................... 179
XXV.	Loss of weight of erosion vent plugs ............... 181,182
XXVI.	Accuracy of life of machine-gun barrels fired at
different temperatures ................................... 19h
XXVII.	Comparison of life of guns and muzzle velocity .... 196
XXVIII.	Calculated accuracy lives of guns .............. 23h
List of Figures
Figure	Page
1.	Typical pressure-time curves .....................«	71
2.	Erosion	of	3-in. gun liner ..................... 10Ц
3.	Erosion	of	3-in. gun after 108Ц rounds	........ 10£
Ц.	Erosion	as	a function of the number of	rounds .... 106
9.	Section	of	the bore surface at the origin	of
rifling of a 37-mm Browning automatic gun M1
after 8032 rounds ........................ 121
6. Interior voids, uneven bore edge and cracks in
37-nim gun СЦЦбС ................................. 12£
7. Hard layer in 3-in. AA gun.No. 138 .................	127
vii
THE EROSION OF GUNS
Part Two: The Characteristics of
Gun Erosion
CHAPTER VIII. MAGNITUDE OF EROSION
59-	The two chief characteristics of erosion are its extent and the
nature of the eroded surface. The exact dimensions of the bore of
a particular gun at any given time depend on so many factors, some
of them uncontrollable, that each gun is a separate problem. On the
whole, however, the erosion of all guns — except those fired extremely
rapidly — follows the same pattern, so that it is possible to des-
cribe these two characteristics in general terms.
60.	Variation along the bore
The increase in diameter of the bore of an eroded gun is not
uniform along its length, but is highly localized at the two ends.
In the middle of the bore, between the two eroded regions, the diameter
frequently is less than it had been originally, because of fouling or
coppering, which is the formation of a metallic deposit on the surface
of the bore (Sec. 67) •
The greatest amount of erosion occurs at the breech end, where
a region of considerable enlargement of the bore extends forward from
the origin of rifling (Sec. 11 ) for a distance of several calibers,
the maximum enlargement being at a small fraction of a caliber in
front of the origin, namely, at the point where the lands had first
attained their full height when the gun was new. The erosion of
the lands is usually two or three times as great as that of the
- 102 -
grooves,—' as is illustrated for a 3-in. М3 gun liner No, 881
in Figs. 2 and 3- The former is a combination of five star-gage
records made at different periods in the life of the gun. the
latter is.a cross-sectional diagram with an exaggerated scale.
Only erosion at the breech end is apparent because that at the
muzzle was so slight in comparison.
In a case gun (Sec. 21) erosion of the centering cylinder
extends toward the chamber from the origin of rifling only as far
as the mouth of the cartridge case. The increase in diameter in
the middle of this region is usually a little greater than that
of the grooves at the origin. In a bag gun (Sec. 21), on the other
hand, the increase in diameter of the centering cylinder becomes
progressively less to the rear of the forcing cone, and is negligible
after a distance of one to two calibers. The chamber does not erode.
Muzzle erosion is always much less than breech erosion, and in
some small-caliber guns it is scarcely noticeable until the end of
life. The maximum increase of diameter in this region occurs at
the muzzle itself. Here the Lands usually wear more rapidly than
the grooves.
Erosion usually is not circularly symmetrical. However, the
dissymmetry is frequent.ly not reported, for one of the two common
types of star gage (Sec. 1Ц) gives only an average diameter, based
Ц8/ Dr. P. R.- Kosting (personal communication, Aug. 22, 19U2)
points out, however, that in a recent endurance test of the 37-mm
gun M1A2.,(see Sec. 107), it had been observed that when double-base
powder was used as the prope.llant the increase of diameter at the
origin of rifling was greater across the grooves (0.035 in.) than
across the lands (0.030 in.) after slightly more than 1200 rounds.
- юз -
on lengths of three radii 120° apart. Some writers have suggested
that erosion of the muzzle is regularly greater at certain positions
around the circumference of the tube (referred to as different
'^•clocks'* in analogy to the positions on a clock face), but such
a generality does not seem to apply to all guns. In three well-worn
155-nnn guns, for instance', in which both vertical and horizontal
diameters were measured, the difference between the twb diameters
across the lands at different positions along the last three caliber
lengths of the gun varied from 0 to 0.03 in., the horizontal diameter
being the greater in two of the guns and the vertical the greater in
the other [Weyher, 1939].
6l.	Variation with number of rounds
The average extent of erosion is frequently measured by the
increase in diameter of the lands at the origin of rifling or just in
front of it. When this increase — denoted usually by E and ex-
pressed in inches — is plotted as a function of the number of rounds,
the typical curve which is obtained for cannon fired slowly shows
that the rate of increase in diameter of the lands at the origin be-
comes less during the later stages of erosion. This relation is
illustrated by Curves A and В in Fig. Curve A which is the
standard curve for an unplated 1li-in./50-caliber Navy gun, has been
expressed by the exponential function,
E = O.3U9 ( 1 - е-0-ОЮО),	(VIII-l)
1l9 /
where N is the number of - equivalent service rounds. — .	Curve В
119/ Naval Proving Ground photograph No. 8302.
2ООг
/го г
u
। e
I <ь
l Ал
is
'l к
/оо
/во -
О
/60
<30
/40
60
/20 -
40
О
юо -
20
&О
О
60 -
•С
Erosion of lands
8}
1
<b
i
<u
i
/034
4o -
03!^
FIG. 2. EZOBIOK OF~ B~IN. GUN L/NE&.
бгооие d/'ometer
J.oSo in. (when necu)
ZO 40	60 SO /ОО /20	/40
Distance from rear face of breech (mJ
Bore d/ameter
z^g,2a 5ooo/n.(<ohenneaj)
• /оо /го /40
3-in. A A Gun /tfB, Liner No. 361
Chamber, о to 235 in.
Forcing Cone, 235 to 24.5 7n.
Bore, 24.5 to /50.57m.
i
О
*
Advance of Ercing Cone (in J
Rounds	Vertical	t-toriz.
229	( not	measured )
292	0.4/	0.36
5Z7	Z.34	2./3
<33/	&.O4-	7.ZZ
/034	11.4е/	//02
EROSION OF LANDS
I.SOO'R
3^"
EROSION OF GROOVES
З.ооо1'
!.540“R
-S-O!
£7g.<3. Erosion of-3-/П.gun offer /084 rounds. 7У1& verfic/e
sco/e is five f/'тез fhe hor/jon/a/ ^sca/e.
— / OG ~
- Ю7 -
represents data for sixty-tiro 133-nim guns, G.P.F., in different stages
of wear [Weyher, 1939].
For a number of 3-in. antiaircraft guns, М3, which had been
fired more rapidly, however, the rate of erosion did not decrease with
^0 /
time. Curve C-—' in Fig. Ц , which shows the increase in diameter of
these guns at the origin of rifling, is slightly concave upward.
Curves A, В and C in Fig. Ц extend to the estimated accuracy
life of the guns considered (see Chap. XIV). Some European guns that
have been fired far beyond this point have shown a subsequent increase
in the rate of erosion, the complete curve in such cases being S-shaped.—
32/
A similar condition has recently been observed— in the case of a
37-mrn AA gun M1A2, which was fired mostly rapid fire (3 or 6 rnd/min).
From round 3000 to round 6800 there was scarcely any change in the pre-
vious increase (0.022 in.) in the diameter of the lands; and then
suddenly the diameter increased 0.0Ц8 in. during the next 1000 rounds.
These data on the variation of erosion with the number of rounds
of the l33-mm guns depend on measurements on different guns, instead
of on a series of measurements at different stages in the life of the
same gun. Hence they may reflect individual peculiarities of the guns.
30/ This curve has been drawn on the basis of star-gage records
in the files of the Ballistics Section, Ordnance Department, U.S. Army.
3l/ P. R. Kosting, personal communication, Aug. 13, 19Ц1
32/ Watertown Arsenal photograph No. W. А. 639-ЦО76, based on
Firing Record No. 8097? P. R. Kosting, personal communication,
Aug. 22, 19Ц2.
- 108 -
The three guns,that had been fired the largest number of rounds
were of French manufacture and of unknown characteristics; the other
five had been made in the. United States at the close of World War I.
One of the latter group showed an excessively high rate of erosion,
but it was suggested that this might have been an erroneous indica-
tion caused by an error in the number (112$) of rounds recorded*
It has been noticed by the present writer that the points
(solid dots) in Fig. 1* representing the increase in diameter of
the bore of these guns (see fourth column of Table XVI) do not fit
at all on Curve B. Instead, it has been found that they fit reason-
ably 1 well on a parabolic curve with a slight upward curvature. There
remains the more likely possibility that the data for the two dif-
ferent makes of gun should be considered to lie on two separate
table XVI. Erosion of 155-mm guns.
Gun No.	Number of	Velocity	Eb	Fc	Loss of	Weight (gm)
	Rounds	(ft/sec)	(in.)	(in.)	Total	Per Round
81*2	'	812	2398	0.037	0.33	1*52	0.56
56?	1609	2383	.062	• 70	590	.1*1*
853		212?	2379	.088	1.06	1023	.U9
.. 1*31* • .	. 11.2^	•	2365 .	.110	2.62	1761	1.57
li 9*	2853	2283	.11*3	5.1*7	2889	1.01
UU*	3289	221*7	. 156	7.33	2725	. 0.83
32*	3597	, 2215 '	.175	8.01*	1*006	1.11
aThe -gun numbers marked with an asterisk indicate those Of
French manufacture (Puteaux). The others were American made.
bE, increase in diameter at origin of rifling.
CF, advance of forcing cone (see Sec. 125d).
dIn the original report [Weyher, 1939] it is suggested that the
number of rounds reported for this gun may be too small. On the other
hand, the steel in this gun may have been of poor quality; for, on the
graph showing the erosion of 62 155-mm guns as a function of the number
of rounds, several other guns showed an equally high rate of erosion.
- 109 -
curves, each of the general shape of Curve B. This possibility does
not seem to have been considered in the original investigation, for
the report [Weyher, 1939] correlates the various measurements as if
the guns were all the same except for the number of rounds fired.
62.	Variation with caliber
The depth of erosion per round and also the maximum depth of
erosion at the end of life increase very greatly with increase of .
caliber. Representative values of the former quantity for several guns
of about the same muzzle velocity but different calibers are given in
Table XVII. It should be remembered that the variation in the rate
Table XVII. Comparison of average erosion per round for guns of
different caliber; velocity, 2500 to 2?5O ft/sec7
Gun	Rounds	Erosion at Origin of Rifling	
		Lands(10-3in.)	Grooves(10-3in.)
37-mm М3 Tube No. 22708	902 to Ш72	0.0Ц7	0.026
3~in. AA Gun М3 No.6Ц0	326 to 528	.17	.12
8-in. Ml888 Mil No. 56	62 to 127	.35	.27
1 Ц-in. M1920 Mil No. 11	123 to 15Ц	1.1	. 96
16-in. M1919 Mil No. 2	123 to 152	2.8	1.Ц
of erosion of guns of the same caliber and muzzle velocity is quite
large, and that therefore the values given in Table XVII should not be
considered as establishing a functional relation between erosion and
caliber. They are merely illustrative of possible values.
- 110 -
63» Advance of the forcing cone—
The forcing cone (Sec^TO) does not retain its original posi-
tion, but gradually moves forward as erosion proceeds. At the same
time the angle of the cone becomes less steep, because of rounding
off of the front, of the conical surface. The advance of the forcing
cone, which is one way of expressing the extent of erosion, is
measured with a special tapered plug gage— that is inserted through
the breech until it is stopped by contact with the forcing cone. The
i .
fifth column of Table XVI lists the advance F of the forcing cone for
some 155-чпт. guns.
6Ц. Weight of metal lost
The weight of metal lost during the erosion of a gun is not
readily determined. It is not directly proportional to the increase
in diameter at the origin of rifling, because the length of the
eroded region increases toward the muzzle at the same time that the
diameter at the origin is increasing. On the other hand, this
forward extension is slower than the increase of diameter, so that
the loss of weight is proportional, not to the square of the in-
crease of diameter, but presumably to some power less than two,
53/ The use of the advance of the forcing cone as a criterion
of the end of life is discussed in Sec. 125(d).
5Ц/ A plug gage that made contact at only two diametrically
opposite points in. the bore was recommended by Weyher [19391j but
subsequent experience at Aberdeen Proving Ground showed that if this
gage were inserted in.the bore at a slight angle, it could be pushed
beyond the forcing cone. Hence its use for routine measurements has
been discontinued. (Arthur E. Jewell, Instruments Section, Aberdeen
Proving Ground, personal communication, Sept. 2, 19Ц2.)
- 111
An estimate of the weight of metal lost from the breech end
of a 155-mm gun tube — that at the muzzle is insignificant --
has been made by the present writer on the basis of the star-gage
records of the guns -listed in Table XVI. The area— under the
erosion curve of the star-gage measurement of the diameter plotted
as a function of distance along the bore was computed separately for
the lands and for the grooves. The space formerly occupied by. the
material eroded away from the lands was considered as being repre-
sented by half the volume of the solid of revolution obtained by
rotation of the area under the erosion curve about the axis of the
bore; and similarly for the grooves. Hence the total volume Vj of
material lost is, according to the theorem of Pappus,
VT = VL + VG = (DA)L + in (DA)g, (VIII-2)
where D is the mean diameter of the section resolved, A is its
56/
area,— and the subscripts L and G refer to lands and grooves,
55/ De Sveshnikoff [1933, p. 659] had measured the area under
the erosion curve of caliber .30 machine-gun barrels with a plani-
meter. He remarked that "aside from giving a general idea of the
dimensional change of the bore at the breech and the muzzle end, the
measurements do not appear to yield information of any value."
56/ The grooves are regularly wider than the lands, sometimes
as much as 25 percent (cf. Table I), Hence the following equation
is more formally correct than Eq. (VIII-2):
VT = Г77 n (DA)l + I ГТ?) " ^G' (VIII-3)
where L and G represent the width of the lands and of the grooves,
respectively. For L/(L+G) = 0.Ц, Eq. (VIII-2) gives a result 10 per-
cent greater than that obtained from Eq. (VIII-3)j but this dif-
ference is scarcely as great as the uncertainties inherent in the
calculation, since no provision can be made for local irregularities
of the bore surface between the points touched by the star gage.
- Ir-
respectively. The corresponding weight of material lost wascom-
puted by the use of a nominal factor of 7«3 gm/cm3 for the density
of steel.
The total weight of metal lost and also the average loss per
round are recorded in Table XVI. It will be seen that the guns
(neglecting No. h3h) may be separated into two groups on the basis
of the rate of the loss of weight. Interpretation of this result
is complicated by the fact that the two groups differed in two
respects, -namely, in the number of rounds fired and in manufacture.
It might be concluded that the rate of erosion, as measured by the
loss of weight, suddenly increased above about 2000 rounds; on the
other hand, it seems somewhat more likely that the two kinds of gun
differed in erosibility (Sec. 61). A definite choice between these
two possibilities cannot be made on the basis of the data available.
What is needed are measurements of the same gun at different stages
of its life.
It was stated by Siwy [1908, p. 67] that a 28-cm gun lost
dbdut 1/3 kg of steel at each round, but he made no mention of the
basis “of this estimate. It seems to be fairly reliable, as indi-
J
cated by a calculation made by the writer of the loss of weight of
57/
a 12-in. (30.£-cm)/L5-caliber Mk. V gun.—' On the assumption that
the lands occupied percent of the circumference of the bore, the
weight lost from the lands alone was Ц10 gm/round. The fact that
$7/ The calculation was based on the erosion curve of the
lands of this gun, published as Sketch No, 1Ц in Naval Ord. [1912],
- 113 -
this gun -was somewhat larger than that referred to by Siwy gives ample
allowance for the weight lost by erosion of the grooves, which would
have been less than that from the lands. It is important to notice
that the rate of removal of metal is several hundred times as great
for this size of gun as for the l55-mm gun already referred to, the
diameter of which is half that of the 12-in. gun.
65.	Scoring
VJhen the surface of the bore of a gun tube has been eroded into
relatively deep troughs, it is said to have been scored. This condi-
tion may result from local imperfections in the steel or, more
usually, it is simply the final stage in erosion that at first was
fairly uniform. The latest report by Kosting and Peterson [19b2]
concerning eroded guns points out that the scoring in the 37-mm gun
M1A2 which they had examined occurred in a region where hot gases
could begin to expand freely after escaping past the projectile before
it started to move forward. This observation seems to confirm the
opinion held in different quarters, which was summarized by Greaves,
Abram and Rees [1929, p. 118] in these words: "It seems probable,
therefore, that scoring begins (if it occurs at all) after some
general enlargement of the bore has already taken place, and is due,
at least in part, to gas-washing produced by the escape of propellent
gases past the driving band during the initial stages of motion of
the projectile."
- 11Ц -
66.	Pastilles
Pastilles are small shallow depressions in the bore of a gun,
ranging in depth from 0.02 to 0.0£ in., and having varying diameters.
They are of two types — bulbous and granular. They were found only
in 7J>-mm guns and in a few l££-mm howitzers, used by both the French
and the A.E.F. in World War I. Scarcely any were reported by the. British
or Germans. None were found in antiaircraft guns [Miller, 1920,
pp. 61 -6I4].
A graph [Miller, 1920, Fig. 20] of the location of £26
pastilles found in 223 7£-™i guns along the bore of the gun showed
that the maximum frequency of occurrence was at a distance of 67. £ in.
from the muzzle,—/ which was near the point of maximum pressure in
the gun. Nearly all the pastilles occurred in the bottom quadrant
of the bore.	(
Two possible causes of pastilles have been proposed. Some
French ordnance inspectors in World War I suggested that unburned
fragments of US No. 3 powder (multiperforated grain), left in the
bore of the gun, detonated by impact of the next shell. Soldiers
operating 7£-mm guns in the field, however, suggested that the tin-
lead anticoppering compound formed a globule of bronze by fusion
with copper and then was pressed into the bore by the next projec-
tile [Miller, 1920, pp. 67, 68, 71]. Neither opinion has been veri-
fied.
£8/ The length of rifling was 87.8 in.
- 115 -
Pastilles have been alleged as a cause of prematures. Hence
they have a great effect on the morale of a gun crew, in some in-
stances causing the crew to destroy a gun which had them. They are
also supposed to reduce muzzle velocity by allowing escape of gas,
and to serve as a starting point for further erosion [Miller, 1920,
pp. 72-7Ы- However, this latter effect seems very doubtful in
view of the findings of Kosting [1936]. As a result'of a compilation
of all essential data on pastilles preparatory to initiating a
metallurgical investigation of them, Kosting found that "the dimen-
sions of the pastilles do not change within the accuracy of measure-
ments (1/6Ц in. approximately) during subsequent firing." For
example, the pastilles in four 153-mm howitzers examined after 23,
177j 307 and Ц11 rounds subsequent to the’original measurement of
the pastille, showed no enlargement. Hence, pastilles probably "
can be safely neglected-as far as erosion is concerned.
67.	Coppering, or metal fouling
The metallic deposit that forms on the surface of the bore of
a gun, usually referred to as copper, is generally considered to
consist principally of metal rubbed off the rotating band. Thus
Tolch [1936a] reported that the copper in a ЮЗ-mm gun consisted of
a mixture of copper and iron oxides in a matrix of free copper. The
analysis showed: total copper, 71.Ц2 percent; total iron, 9.6£ per-
cent; lead, 0.33 percent; and oxygen combined as CuO and FeO, 18.61 per-
cent. The presence of copper is more extensive than a superficial
examination might.indicate, for its surface is frequently blackened
- 116 -
by copper oxide. Heating a section of the bore in a current of
hydrogen reduces the oxide, and then the true extent of the copper-
ing is apparent.
Coppering is greatest in the central section of the bore,
where it may decrease the diameter as much as 0.01 in. In a given
gun it is usually thicker in the grooves than on the lands. It
sometimes occurs on the surface of the eroded section near the
breech. Inasmuch as a deposit in this region is likely to be re-
moved by later firing, it may be the cause of irregularities in the
apparent erosion at that point.
The principal ill effect of coppering is that the movement of
the projectile is slightly less regular. The corresponding irregu-
larity in the rate of burning affects the muzzle velocity of the
projectile and hence its range.
68.	Effect of fouling on erosion
The possible influence of fouling of the bore on erosion was
suggested by Hardcastle [190Ц], who had observed that cupronickel
from the jacket, of the bullet worked into cracks in a caliber . 303
rifle barrel. Its paefcence was shown by immersing a polished
section -of a barrel in ammonia for a week. Hardcastle claimed that
erosion was partially, caused by alloying of the steel with the cupro-
nickel. The. mechanical enlargement of cracks by copper from the
rotating band was considered by Howe [1918] to be an important
cauqe of erosion (see Sec. ?0)«
- 117 -
It has also been suggested— that the zinc in;gilding-metal
bands might have a deleterious effect on the steel of the bore sur-
face, which might explain the observation [Ord. Dept., 1926] that
*
in the first trials of such bands a slight increase occurred in the
erosion of a 3-in. liner, No. 35» The original report on the
firing had suggested that the greater erosion might have been caused
by the increased width of the band. None of these suggestions has
been investigated.
69.	Removal of copper
Copper may be removed from a gun by several methods. Tin,
lead-tin alloy or lead may be mixed with the powder, either in every
round or in special decoppering rounds. Projectiles may be fitted
with rings or disks made of lead-tin alloy. Copper may also be re-
moved by swabbing the bore with an alkaline solution, or by scraping.
The ,British have used tinfoil regularly in ammunition., but the •
American services have not, except for small arms. Within the past
year, however, the U.S. Navy, having found that its guns were copper-
ing badly during sustained rapid fire, has begun the practice of
'	60
adding about 0.2 percent of pulverized lead tb' the powder every round.—'
Coppering of U. S. 37-mm guns in service in "the Middle East has been
reported by the British to be very serious, and they have requested
that the American-made ammunition for these guns be supplied with tin-
foil [O.B.P., 19h2b],
$9/ By Col. G. F. Jenks; personal communication, Aug. 20, 19hl.
60/ Lt. B. D. Mills, personal communication, August 19Ц2.
- 118 -
According to Paquelier [1929], decoppering by the use of
solder is harmful, as shown by some firings of two new U7~n®i guns
at GSvre in 1925. The gun that had been fired with projectiles
having bands of solder had eroded more after 650 rounds than the
other, which had been fired under exactly the same conditions ex-
cept that no solder bands were used. In the one case the muzzle
velocity decreased 13& ft/sec, whereas in the other it decreased
only 79 ft/sec. No other reference to this effect has been found.
- 119 -
'CHAPTER IX. THE ERODED SURFACE
?O. .. The system of cracks
During the firing of a gun the surface of the bore gradually •
becomes covered with.fine cracks which are frequently referred to
as "heat checks." A typical example of them is shown in Fig. 5,—
which is a photograph of a section of the bore surface at the origin
of, rifling of a 37-nm Browning automatic gun Ml after 8O32 rounds^
which таз about the end of its life [Kosting, 19h0]. Just how
early in the life of a gun such cracks begin to develop does not
seem to have been determined.
The pattern of the cracks consists of small areas, nearly
rectangular in outline, that are bounded by two principal series of
discontinuous cracks at right angles to each other. Within each
such rectangle a series of finer cracks forms a separate network.
Another characteristic of the cracks is that they are puckered, so
that they resemble the cracks formed in river-bottom mud when it
dries out in the sun.
Some of the cracks are wider and deeper than others-. On the
lands — shown by the darker parts of Fig. 5 — these prominent cracks
are transverse, whereas on the grooves they are longitudinal.
De Sveshnikoff [1921a, p. 20; 1922, p. 306], -when he noticed this
condition in eroded machine-gun barrels, remarked that these
61/ This photograph and also Figs ..-6 and 7 were obtained for
this report through the courtesy of Lt. Col. S. B. Ritchie and
Dr. P. R. Kosting, of Watertown Arsenal.
- 120 -
directions were the same as those of the tool marks left on the
lands and on the grooves, respectively. Carter [Guion, Carter and
Reed, 1937] also observed that many cracks in a 1,1-in. Navy gun
62 /
started at tool marks. Kosting,--' however, although he does not
deny that many cracks start from tool marks, emphasizes that many
more cracks occur than there are tool marks to start them.
The radial depth of the cracks varies along the length of the
bore, being in general greater toward the breech end. The deepest
cracks of all usually occur where the driving edge of a land meets
a groove. (This side of the lands is toward the top of Fig. 5.)
The depth of the cracks varies considerably in different guns, but
without any apparent regularity. Thus de Sveshnikoff [1933, Table II]
reported that the maximum depth of cracks in 26 machine guns varied
from 0.6 to 3.2 mm, whereas Fay [1916] reported that the maximum depth
of cracks in a 12-in. gun he examined was 1 anm. . Fay also observed
that in the region of greatest erosion in this gun — near the origin
of rifling — the cracks were the deepest and also the fewest. The
number of cracks per inch at the bore edge of a section of an eroded
gun near the origin of rifling was reported by Kosting [ 19Ц0,
Table 7] as 32J? for a worn-out 37-mm Browning automatic gun Ml and
by Kosting and Peterson [ 19h2 ] as Ц01 for a worn-out 37~n®i gun
M1A2. Some of these cracks, which varied in depth from a few
, _ ,	,	. _ , 63/
microns to 0.6 mm, are shown in Fig. 6. —
1
62/ P. RT Kosting, personal communication, Aug. 22, 19h2.
63/ The present Fig. 6 was Fig. 8 in Kosting [19h0].
J
Fig. 5. Section of the bore surface at the origin of rifling of
a 37-nrn Browning automatic gun Ml after 8032 rounds.
I
I
- 123 -
The radial cracks ordinarily are not deep enough to affect the
strength of the tube. Howorth [1910] expressed the opinion that a
split, when it does occur, is an extension of such a crack; this
suggestion was confirmed by later experience at Woolwich Arsenal
[Greaves, Abram and Rees, 1929] with respect to cracked carbon-steel
liners.
The cracks in a ih-in. gun were found by Howe [1918 j Sec. 29]
to be filled with copper, which was covered with a layer of black
copper oxide and dirt. This he removed by heating a section of the
tube in hydrogen. He reported that a 11 careful examination of the
longitudinal and transverse sections indicates that this copper
reaches nearly, if not quite, to the roots of the cracks, but in many
cases it does not reach to their tops, that is, it does not fill them
flush, though from many cracks of the main network, it projects in
the form of a thin network of dikes.” He also found that the copper
color of these dikes could be revealed by rubbing them lightly with
fine emery paper.
The cracks are generally considered to be caused by expansion
and contraction of the surface of the bore, as described, for
example, by Tschernoff [1913] and by Howe.[1 918]. The heating of
the surface of the bore by the powder gases is so rapid that only
a very thin layer of metal becomes hot enough to be in the plastic
state. The expansion of this layer is restrained to two dimensions
by the rigid colder layers beneath, and hence it tends to buckle;
then, after the hot gases have passed, it is quenched so rapidly by
the cold metal beneath that it becomes rigid before it has time to
- 12Ц -
contract to its original state. The volume changes involved in the
thermal transformation of the steel exaggerate the results of normal
thermal expansion.
Lack of ductility imparted by the alteration of structure that
takes place in the surface layers (Sec. 71) is usually assumed to be
a strong contributing factor; but Greaves, Abram and Rees [1929,
p. 117] pointed out that "experiments show that surface cracking of
an intercrystalline character may occur under the action of hot gases
in metals which nill not harden on quenching." At any rate the
cracks are not limited to the altered layer. Their continuation
to several times the depth of this layer was considered by Howe
[1918, Sec. 31] as evidence that they had been deepened by the
"wedging action" of the copper that filled them. Greaves, Abram
and Rees [1929, Fig. 28] also published a photograph showing this
action.
71.	The altered layer
Microscopic examination of the polished cross-sectional sur-
face of a segment of an eroded gun tube shows that the structure
of the metal has been altered for a short distance beneath the sur-
face of the bore. Although the alteration can be seen in an unetched
specimen, it is made more apparent by etching the surface, for
instance with 2-percent nital, which is a 2-percent solution of
nitric acid in ethyl alcohol. Then the altered layer, which does
not etch readily, appears white in contrast :to the rest of the steel,
as shown in Figs. 6(b), 7(a) and 7(b),and hence has frequently
6Ц/ The present Fig. 7 shows photomicrographs obtained by Kosting
for a 3-in. antiaircraft gun similar to those that he published for a
7f?-mm gun [1939b] and a 37-™ gun [19h0].
- 125 -
Fig. 6. Interior voids, uneven bore edge and cracks in 37-mm gun СЦЦбС. The
specimens were copperplated prior to polishing. The bore edge is on top. (a) Un-
etched, showing interior voids in the region of maximum erosion, x 2$,	(b) Etched
with nital, showing cracks and uneven bore edge, x 100; T, troostite bandj W, white
layer; M, martensitic layer, (c) Etched with nital, x 56*0; the horizontal arrow
at the Bottom indicates an incipient crack with grey outline. [Watertown Arsenal
639-2578.]
- 127 -
Fig. 7. Hard layer in 3-in. AA gun No. 138.
The specimen was copperplated prior to polishing.
The bore edge is at the top, as indicated by the
arrows, (a) Unetched, hard layer revealed by
polishing, x 100. (b) Etched with nital for 8 sec,
x 100. (c) Etched with nital for 18 sec, x 100.
(d) Etched with nital for 60 sec, showing the
white band, dark-etching layer and dark-etching
band, x 100. (e) Same as (d), showing two white
layers, x 1 JtOO.” (f) EtchecTwith nital for 30 min 5
the white band is~very complex in places — x 1500.
[Watertown Arsenal, 639-2039.]
- 129 -
been called ’’the white layer." This term seems to have been used
first in a report, Tests Of metals for 1916, probably by F. 0.
Langenberg of Watertown Arsenal, to designate what had been referred
to earlier by Fay [1916] as the "hard layer" and by Howe [1918] as
the "hardened layer." The British writers Greaves, Abram and Rees
[1929] called it the "hardened skin." The illustrations of the white
layer published by de Sveshnikoff [192$, Fig. 1 ], by Lester [l929a,
Fig. Ц], by Greaves, Abram and Rees [1929? Fig. 1] and by Shumate
[1938, Fig. 18], closely resemble Fig. 7(b).
Prolonged etching of the altered layer has been shown by Kosting
[1 939b, 19Ц0] to darken most of it and reveal its composite nature.
The altered layer at a magnification of 100 diameters, as shown in
Fig. 7 (8), consists of a narrow dark-etching layer and an outer
white band, which under higher magnification (x 1$00) is seen in
Fig. 7(e) to be made up of two white layers. The narrow dark-etching
transition band had been observed earlier, for example by Bihlman
[1921], by de Sveshnikoff [192$, Fig. 1] and by Lester [1929a, Fig. 6]
and had been identified by them as troostite.—7^ The resolution of
the main part of the altered layer, however, had not been made before.
Hence in reading and talking about "the white layer" in a gun tube, it
is important to remember that most writers before 1939 were using this
term to refer to the relatively thick white layer shown in Fig. 7(b)
6$/ The term troostite in the past has not had an exact
definition, but has been used to refer to several different types of
microconstituent of steel. The authors cited seem to have intended -
it in the sense of "secondary troostite" as defined by Epstein [1936,
p. 266]. See Table XX for a comparison of this structure with re-
lated ones.
- 130 -
and that Kosting since that date has been using it to refer to the
much thinner layers shewn in Fig. 7(e).
The outer white layer is easily removed by metallographic
polishing, if the surface of the bore is not first protected by
plating it with CoppeiS nickel or chromium. Kosting [1939b, p. 12]
remarked that therefore it may have been absent from some of the
specimens examined by other investigators, because not all of them
adequately protected the surface. The method of obtaining a high
degree of polish of the specimen for examination at very high magni-
fications has been improved by bliss Mary R. Norton [193$, 1937]
at Watertown Arsenal.
72.	Thickness of the altered layer
The altered.layer regularly increases in thickness toward
the breech end of a gun; but, except that it frequently has been
reported as being thicker on the driving edge of the lands, it does
not vary much in thickness around a circumference at a given dis-
tance down the tube. The thickness of the altered layer in a
worn-out gun increases with the caliber of the gun. Greaves, Abram
and Rees [1929, Table 3] compiled a table of the approximate
average thickness of the "hardened skin" for guns of different
calibers studied at Woolwich Arsenal, England, that had fired cor-
dite M.D. This table shows that the average depth at the origin
of rifling in thousandths of an inch is almost equal numerically
to the caliber in inches. A recent measurement by Jones [19Ц2]
of the thickness of the altered layer of the inner "A" tube of a
- 131
16-in. gun—' showed that it varied from 0.0088 to 0.0113 in.
(0.22 to 0.29 mm) in different sections of the bore, but in the
report the variation in depth was not correlated with the location
of the different sections. This altered layer was made up of a
hard layer 0.19 to 0.2Ц mm thick plus a narrow dark-etching band
O.O3I4. to O.OI4.7 mm thick.
The thickness of the four parts of the altered layer — "hard
layer" — were measured separately by Kosting [19I4.O] at 21 places
along the bore edge of a 1-in. section cut from the origin of
rifling of the eroded 37“®ni gun shown in Fig. 5- The results are
summarized in Table XVIII. Another section of the bore located
Table XVIII.
Average thickness of the four parts of the
altered layer at the origin of rifling in
37-mm gun No. .СЦЦбС.^
Layer	Average Thickness	
	(in.)	 (mm)
First (outer) white layer	0.0003	0.008
Second w hite layer	.0002	.00S
Fartensite layer	.0012	.030
Troostite band	.000Ц	.010
* After Kosting [19h0, p. 10].
5 in. from the muzzle of the same gun showed no altered layer. This
result, which has been observed also in other guns, is interpreted
66/ No. S. 15 (Vickers), fired 225 E.F.C. (see footnote 9Ц),
with erosion of 0.633 in. at 1 in. from origin of rifling. The
percentage composition of the steel was: C, 0.26; Si, 0.1^; Mn, O.36;
S, 0.023; P, 0.03h; Ni, 3.60; Or, 0.6£.
- 132 -
by Kosting^X/ to indicate "that wear at the muzzle should be dif-
ferentiated from erosion at the breech end."
In a subsequent examination of an eroded 37-nm gui; И1А2,
No» 109, Kosting and Peterson [19Ц2] found that whereas the entire
altered layer.was about 60 percent thicker than it had been in
37_mm gun No. СЦЦ6С (Table XVIII), the white layer on the average
was only about Ц0 percent as thick as that in the other gun. Also
in gun No. 109 the white layer was seldom complex. These two guns
differed both in composition — No. СЩ6С contained only Ni as an
alloying element; No. 109 contained 2.30 percent Ni, 1.07 percent
Or and 0.31 percent Mo — and in conditions of firing.—/
For a number of machine-gun barrels — the number was not
stated — Snair and Wood [1939, p. 609] reported that
This layer extends for a distance of approximately two
and one-half inches along the bore from the origin of
rifling. It varies in depth along this distance, and if the
depth were plotted versus the distance along the bore, the
resulting curve would closely resemble a powder pressure-
distance curve. This fact establishes a definite relation-
ship between powder pressure developed and layer formation.
This conclusion is open to question, inasmuch as the occurrence of
the maximum depth of the altered layer a short distance in front
of the origin of rifling might more logically be ascribed to a
maximum heating effect there, just as de Sveshnikoff [1921a, p. 18]
considered this to be the cause of a maximum number of cracks at
that point in the machine-gun barrels which he examined. Snair and
67/ Personal communication, Aug. 22, 19Ц2. See also footnote 1.
68/ A detailed history of the firing is not available for
either gun.
-133 -
/
Wood seem to have disregarded the fact that the maximum on the
pressure-distance curve means that -- neglecting localized variations
of pressure within the gas space — the maximum pressure is applied
all along the barrel from the breech up to the base of the projec-
tile at the point indicated and not just at that point alone. Hence
I
"a definite relationship between the powder pressure developed and
the layer formation" would be expected to be accompanied by a depth-
distance curve which was parallel to the distance axis from the
breech up to the point of maximum pressure and which then decreased
toward the muzzle in conformity with the pressure-distance curve.
One eroded gun in which no "nonetching layer" — that is, no
white layer — was found was a Browning machine-gun barrel that had
been fired a total of f?000 rounds in 1$ bursts of 100 to Ц00 rounds
each at the rate of 1000 rnd/min. The interpretation of this result
was complicated by the fact that it was found that the steel inthe
gun was WD 1060 — a carbon steel practically the same as SAE 1060 —
which is seldom used for machine-gun barrels, and that the steel was
very dirty, with coarse dendrites present [Kosting, Carter and Reed,
1937].
73.	Similar altered layer on other steel surfaces
The erosion surface of a gun tube resembles in many respects
surfaces that may be produced by treatment of steel in a number of
different ways. In the gun itself the surface of the chamber __ i,f
a cartridge case is not used — is covered with cracks that differ
from those in the bore only in that the network' is more uniform and
- 13b
lacks the prominent unidirectional cracks which characterize the
surface of the lands and grooves. The structure of the surface is
altered in the chamber just as in the bore.
- The pressure plugs inserted in a 12-in. gun for measuring
the maximum pressure also were found by Fay [ 1916, p. 22Ц1] to
show an altered layer around the edge of the central hole and around
the edge of the plug itself. The surface of the plug was covered
with cracks. Greaves, Abram and Rees [1929, p. 116] used this
phenomenon to study the formation of the altered layer. They placed
cylinders of 0.8-percent carbon steel (pearlitic) in the chamber of
a 15-in. gun .during firing. After one round the altered layer was
0.0037 in. thick, after five rounds, 0.011Ц in., and after 10 rounds
0.0118 in- • The last thickness is the same as that which they
listed for the bore of a l£-in.. gun. A similar altered layer was
reported [Greaves, Abram and Rees, 192 9, p. 11] as occurring "on
the base of proof shot or shell of large caliber, and in fact on
any steel surface on which the propellant gas has acted for a suf-
ficient time."
The surface of an 'erosion vent plug frequently shows an
altered layer — "white layer," in the older sense, — such as
that illustrated by Greaves, Abram and Rees [1929, Figs. 56 to 71 ]•
Among hl alloy steels.tested in erosion-plug experiments and after-
wards examined at Watertown Arsenal [see Sec. 9h(b)], only a few
specimens showed a white layer. These specimens were low in
manganese; with 2 percent or more of manganese, no white layer was
formed. The three steels that showed the most pronounced white
layer contained vanadium [Ritchie, 1928].
- 135 -
A phenomenon that may be related to the erosion of steel by
powder gases is the Munroe effect. During his experiments on smoke-
less powder, Charles E. Munroe discovered that when a disk of gun-
cotton is detonated on a horizontal steel plate, any indentations or
raised characters originally on the under side of the disk are repro-
duced in reverse on the upper surface of the plate [Marshall, 1920;
Browne, 1939, p» 1306]. No metallographic examination seems to have
been made of a steel surface acted upon in this way.
Steel surfaces that have been suddenly heated by friction also
show an altered layer. Greaves, Abram and Rees [1929, p. 116] have
enumerated the following cases with original references:—' (i) steel
rails; (ii) heavily braked railway tires; (iii) wire rope on a pulley;
and (iv) a ball bearing run dry. The heat'checking of the surface of
brake drums, described by Walther [l 938], was explained by him- in much
the same terms as were used in Sec. ?0 for the cracks on the bore
surface of a gun.
Steel can also be eroded by an electric arc. De Sveshnikoff
[1921a, p. 10; 1921b, p. 163] reported that when an electric arc was
struck with either a copper or a carbon electrode against a piece of
gun steel, the area around the central hole produced by the arc
developed a number of cracks and acquired a martensitic structure—
69/ (i) J. E. Stead, Proc. Inst. Meeh. Eng. (1899), p. 77;
W. H. Merrett, Proc. Inst. Meeh. Eng. (190Ц), p. II4.O; J. W. Bampfylde,
J. Photomicrographic Soc. 1Ц, 23(l 927). (ii) H. Brearley, Metal-
lurgist 1_, 132(1925). (iiij E. A. Atkins, J. Iron and Steel Inst. (1927),
p. hh3- A more recent contribution to the third subject is E. M. Trent,
"The formation and properties of martensite on the surface of a wire
rope," J. Iron and Steel Inst. 1ЦЗ, Ц01-Ц19(19Ц1). .
70/ See Table XX for definitions of these structural designa-
tions.
- 136 -
that merged rather abruptly into the original ferrite-sorbite
structure—^ of the specimen. Greaves, Abram and Rees [1929>
Fig, 15>] have also published an illustration of the structure of
the altered layer produced in this way.
Chemical action also can produce an altered structure on
the-surface of steel. Four steel bottles used by the General
Chemical.Company to contain nitrogen and hydrogen at a pressure
of 15>00 Ib/in? and a temperature of $00 to 600°G failed after vary-
ing periods of service. Wheeler [1922, p. 2$71 found that "when
these containers were cut open and the cross-section surface
polished, they showed an inside zone with a different luster from
the rest of the metal. Upon etching, this zone was almost un-
affected while the rest of the metal etched' normally." A similar
alteration of steel was obtained by exposing it to the action of
ammonia at a temperature of 600 to 700°F.
This effect has been confirmed by later investigators. Thus
microscopic examination of a longitudinal section of a machine-
gun barrel made of "nitralloy G" that was nitrided by heating in
ammonia after-machining showed that'a white layer was present
both inside and outside the tube [Lester, 1929b]♦ A white layer
was formed on the surface of specimens of a series of steel alloys
of about the composition of centrifugally cast steel, when they
were casehardened both by nitriding and also by cyaniding [Shumate,
1938]. A white layer similar in appearance to that present in an
eroded gun bore, but much thinner, was formed on a piece of steel
heated in gaseous ammonia at 900°F for 1^ hr. It was suggested
-137-
that the layer in the gun tube is thicker than that produced arti-
ficially by reason of the high pressure in the gun [Snair and Wood,
1939, p. 619]. The appearance of a fused surface that is often
seen in an eroded gun bore was produced artifically by treating a
rough groove in a piece of steel with ammonia at 6J>O°C— and then
rough polishing the piece. A photograph of such a surface at a
magnification of f>0 diameters was published [Wheeler, 1922, p. 296].
Hydrogen at high temperatures and pressures has a marked action
on steel [Inglis and Andrews, 1933j Naumann, 1937]• As pointed out
by Kosting,—^ various types of layer are formed which may vary in
their resistance to attack by common etchants. In some respects some
of these layers are not unlike those observed in eroded machine-gun
barrels.
V. Stefanides, in a discussion printed with the paper by Snair
and Wood [1939] on the white layer, suggested that hydrogen and
water vapor "may play a more important role than they are being given
credit for. The austenite, when formed in the presence of H30, which
evidently breaks down, and the oxygen goes into solution with the
carbides, forms a more stable austenite which is hard to break down,
requiring higher temperatures than austenites without the oxygen in
solution."
71/ The duration of the treatment was not stated; other ex-
periments lasted 20 hr at this temperature.
72/ Personal communication, Aug. 22, 19h2. .
- 138 -
7h. Hardness of the altered layer
Although many writers in describing the bore surface of an
eroded gun have referred to the altered layer as a ’’hardened
layer," few measurements exist to show just how hard it is. In
fact, some of the early metallurgists seem to have considered it
a hardened layer simply by analogy with previously known hardened
layers on tempered steel. Thus Osmond [l901J made no mention of
having determined the hardness of the layer he described.
Fay [1913, p« 133] did measure the hardness, both with a
scelerbscope and with a Brinell ball. Although the results by the
two methods, are decidedly inconsistent, as is shown in Table XIX,
they do indicate a greater hardness at the surface of the bore than
deeper within the metal of the tube. This conclusion was confirmed
by the measurements of Jones [19h2] of the bore of an eroded
:l6**in. gun liner.—/ He found that the hardness at the surface
Table XIX. Hardness of altered layer at surface of bore of
12-in. gun specimens.:	~	’
Specimen		Hardness Number				
No. .	Distance from Muzzle (in.)	Sceleroscope			Brinell	
		Land	Groove	Back®	Groove	Back®
A	0	33 -	27	31	192	170
В	120	3u	28	31	166	156
C	2h0	38	33	31	187	170
D	325	h7	h3	32	187	1h9
E	337	Ц8	Ц8	30	187	1h9
* After Fay [1913, P. 133].
a The reverse side of the trepanned specimen, to indi-
cate the hardness of the unaltered steel.
73/ See footnote 66.
- 139 -
varied from 63O to 633 D.P.H,, whereas at a depth of 0.001 in. below
the surface it was a little greater, from 660 to 710 D.P.H. Measure-
ments at successively greater depths showed thatthe hardness decreased
uniformly with depth until below 0.009 in. the hardness was 260 D.P.H.,
that of the unaltered steel. Shumate [1938> p. 22] reported that he
was not able to measure with certainty the hardness of the altered
layer on the'surface of the bore of an eroded liner for a 103-mm gun,
using a Vickers hardness tester.
Greaves, Abram and Rees [1929, P« 116], instead of measuring
the hardness of the altered layer on the bore surface itself, measured
the hardness of the layer produced on steel cylinders placed in a
l3_in. gun (Secs. 73 and 7З). After the cylinders had been fired
ten rounds, the Brinell hardness, measured with a 1-mm ball and 30-kg
load, had increased from 209 to 3h7-
The scratch hardness of the altered layer was determined roughly
by Bihlman [1921, p. 3]- He found that a scelerometer scratch
З.Ц microns wide on the unaltered steel surface was reduced to 2.8
microns in width where it crossed the white layer. A photomicrograph
of a similar scratch but without a measurement of its width# was
published by de Sveshnikoff [1923, Fig. 3] , who remarked (p. 796)
that it '‘showed that this surface layer was considerably harder than
the original steel."
The only indication of the hardness of the thin outer white
layers are photomicrographs of a scratch across the white layers in a
73-mm gun [Kosting, 1939b, p. 13] and a Bierbaum microcharacter scratch
across the white layers in a 37-mm gun [Kosting, 19h0, Fig. 7(b)]. The
- що -
former photograph was said to show that “the outside of the white
layer is slightly harder than the inside."
75. The altered layer considered as martensite—/
Examinations of the altered layer were made first by metal-
lurgists, who tried to explain the hardness of that layer in terms
of some process already known to cause hardening of a surface layer
on a piece of steel. Fay 916] summarized the three possibilities
as (i) cementation, (ii) heat treatment, and (iii) cold-working.
He ruled out the presence of free cementite, because the hardened
layer did not etch when treated with boiling sodium picrate. He
assumed instead that the surface layer was heated considerably
above Acx andthen chilled rapidly to martensite by the cold layers
below the surface. Although no needles of martensite were found,
it was concluded that the foregoing assumption was verified by the
fact that the altered layer could easily be changed to troostite by
tempering. As a result of experiments with pressure plugs that
were locally cold-worked and then fired in a gun, it was concluded
that cold-working, as by the rubbing of the projectile on the
driving edge of the lands, was an essential part of the hardening
process.
Fay and'various later writers quoted Rosenhain and Beliew
[1913] in support of the view that the altered layer consisted of
martensite; but these citations are of little worth because they
 refer simply to separate statements, made during a discussion at
a Scientific congress, that a distinctly martensitic structure had
Th/ The several terms used in describing the metallographic
structure of steel are defined in Table XX and the notes that
accompany it.
- 1h1 -
been observed. There -was no opportunity at that time to support
the statements by photographic evidence, and none seems to have been
published since then by these investigators.
Howe [1918] followed Osmond [1901]in considering that the
altered layer was either troostite or martensite, depending on the
extent to which the alteration had proceeded, the troostite being
an intermediate stage. Bihlman [1921, p. 3] was in general agree-
ment with this conclusion, for he reported that photomicrographs at
2^0 diameters showed a structureless white layer on the surface, a
dark-etching layer immediately behind it and then the original
structure of the steel. "The characteristic structure of martensite
was not observed in the white layer of any of the specimens examined";
but a determination of the relative scratch hardness of the altered
layer (Sec. 73) was said to "bear out the suggestion of Fay that the
edge structure is a martensite-troostite-pearlite one."
Greaves, Abram and Rees [l929, p. 116] adopted the same general
view. They described the "hardened skin" on the surface of the
cylinders that they fired in a 1fj-in. gun (see Secs. 72 and 73) as
consisting of layers of different structure, as follows: (outside)
coarse martensite, fine martensite, troostite, ferrite and troostite,
narrow sorbitic region, and, finally, original structure.
As a result of his chemical, microscopic and x-ray examination
of a worn 16-in. gun (see Secs. 72, 7h, 77), Jones [19ц2] concluded
that the hardness of the altered layer was caused by the formation
of martensite, as evidenced by the observation that the alpha-iron
lattice was distorted to an unusual extent and that this distortion
- 1Ц2 -
Table XX. The microstructural oonatituent» of steel. Thia table ia baaed on data
obtained from Epstein [1936, Chap. VIII], Evana [1?39, PP. 150-11 and a private communi-
cation from the reaearoh laboratory of the U.S. Steel Corporation.
- Tl+3 -
Notes on Table XX
The allotropic transformation between the gamma and alpha forms
of pure iron takes place at a slightly different temperature on heat-
ing than on coolings The former temperature (910°C) is designated as
Ac3 arid the latter as Ar3, which are abbreviations for the French ex-
pressions arret sur chauffage and arret sur refroidissement,
respectively, in reference to the breaks on the heating and cooling
curves» The Curie point of alpha-iron (about 768°C), above which the
iron is paramagnetic instead of ferromagnetic,- is designated as A2.
The gamma-alpha transformation- of the iron in steel does not
take place at a fixed temperature because it is accompanied by a re-
action between the iron and the carbon. Thus on slowly cooling a
hypoeutectoid steel — that is,- one containing less than O.87 per-
cent C. — from above 91O°C, the transformation begins at Ar3/ As
it proceeds, ferrite is formed and the austenite solid solution is
enriched in carbon until the composition of the eutectoid between
ferrite, austenite and cementite is reached at O.87 percent C. Mean-
while the temperature falls until that of the eutectoid line is
reached. If equilibrium is maintained, the remaining austenite then
transforms to pearlite at this temperature, which is designated as
Arx (723°C).-
In the system Fe-C, when austenite is quenched the gamma-alpha '
transformation .takes place; but the precipitation of the excess
carbon is inhibited. The presence of this excess carbon causes the
crystal lattice of the alpha-iron in the resulting martensite to be
distorted to tetragonal symmetry. Certain alloying elements that
may be added to steel cause the transformation as well as the pre-
cipitation to be inhibited, with the result that nonmagnetic austenite
can be stabilized at ordinary temperatures.
Then martensite is tempered by heating, the lattice distortion
of the alpha-iron is removed by the formation of ferrite and the pre-
cipitation of the .excess carbon as cementite. The secondary troostite
or sorbite that is thus produced contains the same proportions of
ferrite and cementite as the pearlite or primary troostite that might
have been formed from the original austenite by slow cooling or rapid
cooling, respectively; but they differ from it in microstructure.
Bainite is a separately distinguished primary structure that is formed
by the process of austempering, in which austenite is quenched to the
intermediate temperature range 2OO-f>f>O°C and then isothermally trans-
formed.
The adjectives ’’primary” and ”secondary”' are frequently omitted in
references to troostite, the context indicating which type of structure
is meant. The troostite mentioned in the various papers on the altered
layer is secondary. This constituent is now considered by the research
laboratory of the U.S. Steel Corporation as merely a special variety of
sorbifee and is- not separately named.
Ap especially useful, equilibrium diagram of the system iron-carbon,
containing much detailed information, was published by Sauveur [1935,Р»Ь6?
- 1ЦЦ -
was removed by heating to ЦОО°С in a vacuum. X-ray examination of
an eroded Bren machine gun that had been fired Ц000 rounds at
100 rnd/min also showed distortion of the alpha-iron lattice, but
to a less extent than in the 16-in. gun.
76. Carburization as a factor in martenization
Although de Sveshnikoff [1925] agreed that the altered layer
consisted of martensite and troostite, he maintained that its
formation involved not only quenching but also carburization of the
steel at the surface of the bore by the powder gases. V/hereas
Vieille [1901, p. 219], who had suggested this possibility to ex-
plain the hardening of the surface of erosion vent plugs, had been
merely speculating, de Sveshnikoff based his conclusion on analyses
of chips reamed from six eroded machine-gun barrels made of dif-
ferent steels.—' Two successive cuts 0.00Ц or 0.005 in. deep
were made for a distance of 1.5 in. forward from the origin of
rifling. The samples obtained by the first cuts showed increases
in carbon content ranging from 30 to 183 percent, compared with
that of cores drilled from the main body of the steel. The samples
obtained by the second cuts showed increases of only 1h to 33 percent.
Fay [1925], in commenting on the work of de Sveshnikoff,
amplified his former theory by agreeing that absorption of nitrogen
and of carbon accelerated the formation of the hard layer, since in
the meantime he had found out [Fay, 1921 ] that ’’steels are nitrogenized
75/ These were some of the barrels made of special steels, the
trial of which is described in Sec. 92.
- 11+5 -
as well as carburized in casehardening operations, the absorption of
nitrogen preceding that of. carbon." Graziani [1928] also supported
the view that carburization is a cause, of the hardening of the sur-
face of the bore..
Piantanida [l922], on the other hand, while he admitted that
the altered layer consisted of martensite, denied that it was caused
by carburization, because it disappeared on annealing. Later he
examined guns (caliber not stated) that had been fired to the end
of life. He annealed sections of the bore by heating them to 900°C
in a slow stream of hydrogen or nitrogen in an electric furnace and
allowing them to cool slowly in the furnace. Whereas unannealed '
sections showed a distinct altered layer, the annealed ones did not.
Furthermore, the number of pearlite grains was no larger near the
surface of the specimens than it was at a greater depth. Hence it
was concluded that the altered layer had not been caused by carburiza-
tion [Piantanida, 1935].
77» The altered layer considered as a nitrided layer
An entirely'different explanation of the altered layer was given
by Wheeler [1922]. From a comparison of the appearance of the white
layer found on the surface of steel nitrided in an atmosphere of
ammonia with that found on the bore surface of a gun, he concluded
that the latter was a locally cold-worked austenitic case due to
penetration of nitrogen.. He argued that
Since nitrogen under pressure and with heat penetrates and
combines with steel as has been described, it would be strange
indeed if the reaction did not occur on the bore of a gun
where there is an atmosphere of from 35 to Li5 percent nitrogen,
- 1Ц6 -
very hot and fresh from combination of another sort and
therefore nascent and under a pressure of 30,000 to
Ц3,000 Ib/in? Since even molecular nitrogen is known to
react at 5>00°C and 15>00 lb/in?, the reaction must occur
in a gun. By assuming that the white layer on the inside
of a gun is the same as that which can be artificially
produced by nitrogen, most of the loose ends of previous
theories are picked up.
The same samples of material from the surface of the bore of
machine-gun barrels that he analyzed for carbon (Sec. ?6) , de
Sveshnikoff also analyzed for nitrogen. Although the nitrogen con-
tent, which was of the order of a few hundredths of 1 percent, was
higher than normal for these crucible steels, it was ’’altogether
too low for assumption that the white layer consists of iron
nitride. ” It was considered that ’’nitrogenization may or may not
be concomitant with carburization," depending on the presence of
particular alloying elements, such as chromium, that have an affinity
for nitrogen. Also, it was argued, the fact that it had been pos-
sible to change the white layer to a dark-etching one by heating it
to 320 or 3?0°C proved that it "could not be a nitride of iron be-
cause iron nitride does not readily decompose below Ц5>0°С." He
did finally concede tliat "the probability of absorbed nitrogen
remaining in the solution should not be neglected, since in such a
case the layer may have a martensitic character and change at
temperatures below the decomposition temperature of nitride."
In rebuttal to de Sveshnikoff, Iliheeler [l92$] pointed out
that he had not claimed the presence of iron nitride in the altered
steel but simply of a solid solution of nitrogen in steel. He
i
remarked that the nitrogen in solid solution would not have been
determined by the analytical methods used by de Sveshnikoff. After
- Шт -
he had suggested that the specimens analyzed might have included
foreign matter Containing carbon or nitrogen, he Went on to argue
that even if the altered layer contained more carbon than the un-
altered steel, his nitrogen theory was not invalid. He considered
that "whether partial carburization or decarburization takes place
is a matter of no great consequence, dependent simply upon the con-
centration of carbon and hydrogen in the gases."
The suggestion that the altered layer might be the result of
nitriding was supported by Lester [1929a] as a result of a micro-
scopic and x-ray examination of rings from the same 12-in. gun that
had been studied by Fay [ 1913; see Sec. 7h] compared with a similar
examination of an eroded caliber .30 machine-gun barrel that had
been made of nitralloy and then nitrided by the usual commercial
procedure [see Lester, 1929b].	Polished cross sections of the two
guns showed similar structures under the microscope. The x-ray
diffraction patterns of sections from both guns showed the spectrum
of alpha-iron with the lines displaced to a slight extent, indicating
an enlargement of the lattice of 0.3 percent. The section from the
12-in. gun showed also a spectrum of gamma-iron that was almost as
strong as that of the alpha spectrum (see Sec. 79); but the section
from the nitrided machine-gun barrel showed no gamma spectrum. It
was concluded, therefore, that the white layer in the 12-in. gun
contained about Ц0 percent of austenite, "caused by the alloying
effect of nitrogen with consequent lowering of the Arx point to such
an extent that the solid-solution phase is formed on the surface,"
as explained by Wheeler [1923, p. 800]. The lack of a similar
- 1Ц8 -
austenitic phase in the case of the machine-gun barrel was explained
on the ground that there had been less opportunity for quenching.
The hardness of the altered layer was claimed to have been the
result of the lattice distortion, which in turn was ascribed to
the presence of nitrogen in solution, both in ferrite and in austenite.
Confirmation of the x-ray diffraction pattern described by
Lester was reported by Snair and Wood [1939], who also found a dis-
tortion of the lattice of alpha-iron of O.h9 percent in an exam-
ination of the eroded surface of machine-gun barrels. Although they
concluded that the white layer was a nitride, they had no other
positive evidence than this agreement with Lester's previous deter-
mination of the lattice enlargement of a nitrided barrel. They did
find that wrhen a sample of the bore surface that showed a distinct
white Layer was heated for 1 hr at ЦОО°С and cooled in the furnace
to prevent quenching, the white layer remained white. They claimed
that this result showed that the white layer was not martensite,
bocause martensite would have broken down and would have appeared
dark after the heat treatment, which was exactly what Bihlman [1 921]
and de Sveshnikoff [1923] claimed that they had observed.
The nitrogen contents of successive layers of steel 0.001 to
0.002 in. thick, removed with dilute hydrochloric acid from the
bore of an eroded 16-in. gun, J—/ were determined by chemical
analysis by Jones [ 1 9Ц2].	He found that in three sections ex-
amined the amount of nitrogen decreased gradually from a maximum of
76/ Soo footnote 66.
- 11+9 -
0.11 to 0.18 percent in the surface layer to about 0.008 percent in
the core metal at a depth of 0.01 in. The maximum amount of nitrogen
in the surface layer was very much less than the 9 to 10 percent that
Jones and Morgan [1932] had found in the surface layers of nitrided
steels and considerably less than the 1 percent they had found at a
depth of 0.011 in. In x-ray diffraction photographs of successive
layers of similar sections from the same 16-in. gun Jones [19h2]
observed a very faint set of lines, which indicated the presence of a
small amount —/ of solid solution of nitrogen in gamma-iron; but he
found no evidence whatever of Fe^N and Fe^N, which he claimed '’give
particularly strong characteristic spectra when a steel is hardened
by the process of nitriding.” He therefore concluded that the
hardening of the altered layer was not caused by nitriding. Instead,
as mentioned in Sec. 7^, he attributed it to the formation of
martensite.
78.	Relation of cracks and inclusions to the altered layer
Photomicrographs published by Kosting [ 193 9b, 19Ц0] show that
some of the deep cracks that penetrate into the unaltered steel are
lined by the white layer along their upper* surfaces. Other photo-
micrographs (Figi ^(cj, for example) show the birth of such a crack.
To what extent the formation of the cracks was accelerated by the
white layer is unknown. Inclusions, on the other hand, definitely
77/ In sections of an eroded Bren machine gun which he also
examined by means of x-rays, Jones found relatively larger amounts
of gamma-iron containing nitrogen, perhaps as Fe^N.
- 150 -
seem to., accelerate the deterioration of the surface of the bore.
Kosting [19Ц0, p. 8] reported that photomicrographs ’‘show that
where a radial crack and inclusion intersect, the crack branched
and followed around and finally enveloped the inclusion with a
marked effect on the surrounding steel." Other photomicrographs
"show that inclusions to which gases had access, and which were
adjacent to or within the hard layer, facilitated marked change
in the steel and loss of metal at the bore."
79.	Significance of the outer white layers
The work of Kosting that reveals the previously-unsuspected
complexity of the altered layer may represent the means of bringing
together the somewhat divergent viewpoints with respect to the
nature of that layer. He agrees with the early workers that most
of it is martensitic and is joined to the unaltered steel by a
troostitic transition zone. At the same time he considers that
the two white layers which he has found on top of the martensitic
band indicate the occurrence of "a chemical change on the surface
that results, in the case of the present steels, not only in the
formation of a friable layer that spalls off in thickness of the
order of magnitude of 0.000^ in., but also in the selective attack
by some agent that penetrates the steels, resulting in cracks and
leading to pitting and the loss of metal in large chunks" [Kosting,
1939а]. If this chemical reaction were a nitriding one, as Kosting
himself has suggested it might be,—z the two principal points of
78/ Personal communication, August 19Ul.
- 131 -
view concerning the nature of the altered layer would be recon-
ciled.
The identity of the two white layers is still unknown. '
Kosting,[ 1 93 9a ] reported that an x-ray diffraction pattern obtained
from the bore surface of a V^-mm gun showed the spectra of both
alpha- and gamma-iron, and also some unidentified lines (see Sec. ?6).
The white layers do not seem, to be constant in their properties, the
two layers being less sharply separated in some cases than in others
[Fig. 7(f)]. The significance of variations in the white layer that
Kosting [19h1, p. 19] reported he had observed in some other guns
is not fully understood. It is possible that the white layer adjacent
to the martensitic band represents a zone in which the reaction be-
tween the steel and some constituent of the powder gases is still
incomplete, and that the easily detached outer layer represents the
end product of that reaction.
- 1$2 -
CHAPTER X. EXPERIMENTAL METHODS OF STUDY OF GUN EROSION
80.	The experimental study of the erosion of guns is performed
most directly by actual firing under controlled.conditions. Such
a test is both expensive and time-consuming; therefore the need
has long been felt for a means of reproducing erosion on a small
scale. Erosion plug tests have been performed in the past fox* this
purpose, but without complete correlation of the results with those
of firing tests. Tests with explosives in closed vessels give little
information concerning erosion, Within the past year a laboratory
"gun” has been developed at Battelle Memorial Institute, and there
is some hope that it may more closely reproduce service conditions.
8l• general description of firing tests
.A firing test for the study of erosion consists of firing a
gun until erosion has proceeded so far that the gun is no longer
serviceable. Usually several guns are fired in the same test,
each.gun (or group of guns) differing from the others in only one
particular,, such as the kind of steel in the tube, the type of
projectile or the kind of propellant. Throughout the test, which
lasts for several days with a major-caliber gun, all conditions of
firing are kept as uniform as possible. At periodic intervals the
velocity of the projectile is measured during a series of rounds
and the accuracy of. .the gun during anpther series. In most tests
the. gun is cleaned periodically and the bore is star-gaged in order
to obtain a record of the progress of erosion. In some tests>
other measurements, such as the maximum pressure or the temperature
- 153 -
of the tube, are made from time to time. The final result of the
test is the rating of the accuracy life of each gun. The differences
among them are correlated with the variables being tested, with the
help of the measurements made during the test. Frequently each
variable in the test is represented by only one or two guns, in
which case the interpretation of the results is somewhat uncertain,
because the reproducibility of the measurements is not very high.
The variation in the performances of two guns that are presumably
the same may be almost as great or even greater than that between
guns of different design.
79/
82.	Гetermination of accuracy life of guns-—z
The accuracy of a gun is' determined by firing at a target.
There is no complete agreement, however, as to the criterion to
be used in measuring the accuracy. The mean deviation and the extreme
deviation from the center of the target have both been used. The area
of the smallest ellipse or circle that encloses all the hits gives
another measure. The ellipse is preferable to the circle, because
the deviations are likely to be arranged along some line as an axis.
In the firing of small arms the end of life is often considered
to be indicated by the occurrence of a. specified number of ''keyholes"
or "tips" on the target — say three in twenty rounds. A keyhole,
which is a hole of that shape in a paper target placed at fairly close
range, indicates that the bullet passed sideways through the target.
79/ See Chap. XIV for a discussion of the life of guns under
service conditions.
- 15Ц -
е
A. tip is an ellipsoidal hole in the target that indicates that the
bullet was yawing—^ considerably (but less than 90°) at the
moment when it passed through the target. A bullet that makes a
tip would make a keyhole in a target placed farther away, at a
distance depending on the rapidly with which the bullet is
tumbling. A bullet that makes either a keyhole or a tip in the
target would, of course, be very erratic in flight at normal range.
The regular occurrence of tips or keyholes is a clear indication
that the bore is so badly eroded that some of the projectiles can
pass through it without being properly engraved by the rifling
(Secs. 8 and 18) and hence that the barrel lias really reached the
end of its usefulness [see Sec. 12£(e)].
83.	Cost <x£ .firing tests
A firing test of ? special kind of tube or of some other
special feature requires, in order to be reliable, a minimum of
four tubes —• two regular tubes for control and two special tubes.
For each additional variable at least two more tubes should be
tested. The test of four tubes would require the services of about
9 men: 2 to operate the gun, 2 to measure the velocity, 3 to deter-
mine the accuracy, 1 to star-gage the guns and 1 to supervise the
test. The firing of four guns would occupy 15> to 20 days; but the
over-all time of the test, including the compilation of the data,
would be about three months. The cost of the ammunition required
80/ The' angle of yaw of a projectile is the angle made by
its axis of symmetry with the direction of its motion.
- 155 -
to fire a'tube to destruction by far exceeds both the cost of the
tube itself and also the cost of the personnel*needed to carry out
the test. Estimates of this cost for four sizes of.guns are given
in Table XXI.
Table XXI. Estimated cost of ammunition needed for firing
guns to destruction.
Gun	Estimated Life (rounds)	Projectile	Ammunition for li guns (complete rounds)*	Cost (dollars)
Caliber .30 MG"	8,000	Ball	Ц8,000	. 1600
37_mm, М3	3,000	HE .	18,000	75,200
l55~mm, Ml	2,000	Bnpty for sand loading	12,000	632,000
16-in.,М1919M3	175	AP, empty for sand loading	1,050	2,088,000
* The number of complete rounds required has been estimated
by taking one and one-half times the figure given in the Ordnance
Proof Manual for the estimated accuracy life, in order to insure
that enough ammunition would be available to fire the guns to the
end of life, even if some of them exceeded the nominal estimate.
8Ц. Erosion vent plug tests
The erosion vent plug test was introduced by Noble in 1882
for the purpose of studying the relative erosibility of various
steels by gunpowder, later it was used by Vieille [1901] to compare
both the erosibilities of steels and the erosiveness of different
smokeless powders. The method has continued to be used from time
to time by other investigators. Their results will be discussed
in Secs. 911 and Ю9.
- 15>6 -
 The explosion bomb— that is commonly used for erosion
vent plug tests.is arranged with three openings. One is fitted
with an electric connection for firing the powder by heating a
wire to incandescence; a second is fitted with a pressure gage
(Sec. 89); and the third is airranged so that a cylindrical test
plug with a small axial hole can be inserted 'into it. The gases
formed when a charge of powder is fired in the bomb escape through
this hole with high velocity and enlarge its diameter.
The extent of this "erosion" is usually determined by
measuring the loss of weight of the plug. Sometimes the loss per
unit weight of powder is recorded directly; at other times it is
transformed into the corresponding loss of volume of material.
Greaves, Abram and Rees [1929] expressed their results in terms
of the slope of the (approximately) straight line obtained when
the loss of weight was plotted against the maximum pressure.
The erosive action in a vent plug test is so great that only
a single firing is needed to obtain a measurable loss of weight.
For a plug having a 2-mm vent 28 mm long, for instance, a charge
of 3100 grains (20Ц gm) of cordite Li.D. fired at a maximum pres-
sure of about 2300 bars (33,000 Ib/in?) caused a loss of $ to
13 gm, depending on the composition of the material of which the
vent plug was made [Greaves, Abram and Rees, 1929, Table III].
81/ One such bomb and the results obtained in testing a
wide variety of materials are described in a forthcoming NDRC
report by 0. H. Loeffler and G. Phair entitled Metals tested as
erosion vent plugs.
157 -
It seems certain that much of the erosion of a Vbnt plug occurs by
reason of actual fusion of a surface layer of metal; but to what
extent any other mechanism, such as the friction of the powder* gases;
plays a part is not known.
85.	Effect of conditions of vent plug test
Vieille [1901] made a study of the effect of variation of the
conditions under which an erosion vent plug test is carried out. He
reached the following conclusions, which have been verified by later
workers.
(a)	Diameter of vent. A given charge of powder produces
less erosion the larger the vent, except for extremely small vents»
The decrease is not entirely attributable to the lowering of the
maximum pressure, because there is much less erosion of a 2-mm vent
than of a 1-mm one, although the maximum pressure is nearly the same.
Vieille [1901] and de Bruin and de Pauw [1931] used a vent 1-mm in
diameter, but Greaves, Abram and Rees [1929] used a 2-mm vent, and
«
the plugs tested at the U.S.Naval Proving Ground had Ц-mm vents
[Bu. Ord., 1931].
(b)	Length of vent.- The erosion is greater the longer the
vent. Thus the loss of weight of a plug having a 1-mm hole Ц0 mm
long was two and one-half times as great as one having a hole of
the same diameter only 10 mm long.
(£) Quantity of gas. — By firing the same size of vent
plug in bombs of different dimensions, it has been found that tho
erosion per gram of powder is greater the smaller the charge.- This
is explained on the ground that the increase of diameter of the vent
- if>8 -
caused by the initial erosion slows down the rate of.erosion during
the later stagesj so that the latter part of a large charge is less
effective than the same-amount of powder would be if fired as a
separate charge through a new vent,
(d)	Pressure. The erosion produced by a given mass of
gas, which had been almost negligible, at a pressure of 100 bars,
became considerable when the pressure was increased to 2000 bars;
but then it scarcely increased any more when the pressure was
raised to Ц000 bars.
(e)	Repetition of firing. — When the same vent plug is
used for a number of successive firings, the amount of erosion
decreases gradually, both because the diameter of the vent is in-
creased and also because the maximum pressure is less.
86.	Influence of turbulence on erosion of vent plugs
The experiments of de Bruin and de Pauw [1931], in addition
to confirming the foregoing conclusions of Vieille, showed that
turbulence of the gas stream is a very important factor in the
erosion of a vent plug. They used segmented plugs made up in
three sections, in order that the turbulence might be modified
by varying the diameter and the length of the middle section.
In one experiment, for instance, the effect-of turbulence
was clearly shown by using a plug that had a middle section $ mm
long with a hole 7 mm in diameter, while the two end sections
were 10 mm.long and had holes only 1 mm in diameter. When this
plug was fired, using a l|0-percent nitroglycerin powder at a maxi-
mum pressure of about 1Ц00 bars, the third section of the plug
- 159 -
eroded more than the first, even though the gas had lost some of:
its energy by the time it reached the third section.
They also found that if the end sections of such a segmented
plug were renewed after each round, repeated firing produced a
cavity in the middle section that was of the same general shape
even though the initial diameter and length of the middle section
were changed. The characteristic form of the cavity was an
elongated ellipsoid. Thus with end sections 10 mm long having 1-mm
holes, the particular charge of powder that was used created a
cavity about 20 mm long and 6 or 7 ram in diameter. at its widest
part. It was found that after this characteristic cavity had been
formed, the rate of erosion decreased considerably. Hence de Bruin
and de Pauw concluded that the outline of the cavity represented
the streamlines of the gas as it issued from the orifice of the
first section of the segmented plug, and that once this form had
been achieved, no more turbulence occurred and hence there was
scarcely any erosion.
87.	Applicability of erosion vent plug tests to gun erosion
Various writers have pointed out that care is necessary in
drawing conclusions concerning the erosion of guns from the results
of erosion vent plug tests. Thus H. F. Leary [Bur. Ord., 1931],
then Inspector of Ordnance in charge of the Naval Proving Ground,
although he stated that "the Proving Ground believes that erosion
plug tests offer the quickest and most economical method of deter-
mining the suitability of a steel for gun use," nevertheless, on
- 160 -
the basis of comparative tests against standard samples, sum-
marized a memorandum on the relationship of erosion plug tests to
gun erosion in the following words;
The results of the erosion plug tests necessarily have to
be considered, in relation to erosion in guns, as showing
a tendency towards significance rather than as being sig-
nificant in themselves. This is caused by the elements
of difference between the two conditions. The period of
application of heat, the fundamental significance of the
pressure and the quantity of metal eroded in the two
cases are radically different.
On the basis of a critical comparison of the data from ero-
sion vent plug tests published by Greaves, Abram and Rees [1929]
with those obtained at Aberdeen Proving Ground and at the Naval
Proving Ground, P. R. Kosting [1931b 1938} chemical engineer at
Watertown Arsenal, concluded that
This is not a sensitive test to differentiate metals.
On the other hand, when used to rate gunpowders upon
their erosive effects, parallelism between such tests
and service tests appears to exist. Before discarding
the test, its mechanism should be empirically studied,
for it is believed that it has a bearing on the erosion
of grooves. A metallographic study of the container,
within which the explosions occurred, should be under-
taken, for it is believed that more important data will
be obtained than the weight loss of the plug.
Even de Bruin and de Pauw [1931] concluded the account of
their extensive experiments with erosion vent plugs with the
following admonition:
If one is to apply conclusions.from tests of this
kind to the construction of guns, he must be very care-
ful, inasmuch as these tests differ greatly in many re-
spects from actual firing. Hence it is recommended that
only the most general conclusions be drawn, for they are
the only valid ones that these tests offer.
- 161 -
In view of the results that have been obtained in the course
of years with erosion vent plug tests, the following generalisation
seems to be justified; namely, that no metal which is eroded badly
in an erosion vent plug test would be satisfactory for a gun tube
or barrel. Hence the test may have some value in the preliminary
evaluation of new materials proposed for tubes or barrels. Even
if it would not distinguish the best, at least it would eliminate
the worst.
88.	Battelle Institute laboratory erosion gun
At Battelle Memorial Institute a gun lias been developed to
furnish a convenient means of producing erosion in a small test
barrel, which is a cylindrical tube of whatever material is being
tested, 1 in. long and 0.^0$ in. in inside diameter, with a wall
thickness of 0.27 in. The projectile consists of two parts. One
piece is a carefully machined solid cylinder about 2 in. long that
fits into the barrel. The exposed end of this part of the projectile
is screwed into a 19-lb cast-iron weight which slides in a frame
between two vertical oak strips that act as a brake by being par-
tially compressed by heavy coil springs. The projectile is fired
by a solenoid-operated firing pin which sets off 1 gm of 37-пий powder
contained in a 12-gage shotgun cartridge case that has been cut down
to a length of about 3/h in. The powder is held in place by one of
the regular shotgun wads. Under these conditions the maximum pres-
'l	.	*
sure is about 11,£00 Ib/in? and the projectile,attains a muzzle
velocity of h0 ft/sec. The gases are in contact with the test
barrel for about O.OO36 sec.
162
The standard procedure adopted after preliminary experiments
•was as follows. The barrel and its projectile were ground until
the diametral clearance was 0.005 in. They were fired a total of
Ц00 rounds at a slow rate of fire — 1 rnd/min or slower. After
each group of 25 rounds., the barrel was cleaned, weighed and photo-
graphed on the inside. At the end of firing, measurements of the
wall thickness were made at a considerable number of points^, from
which a contour map of the inner surface was drawn.
With this gun a wide variety of metals and of steel plated
with different metals have been tested. The results have been
described in a series of monthly progress reports [Russell,. 19h1a]
which contain photographs of the eroded areas. The materials
tested have been classified [Russell, 19Ц1b] as follows, on the
basis of the loss in weight of the barrel that resulted from the
firing of Ц00 rounds in the laboratory gun;
(a)	Bad materials, loss 0.23 to 0,li3 gm. — Austenitic
steels, including the particular steels selected for their re sistr-
ance to heat checking in hot-dye work; massive nickel; massive
copper; nickel plate; copper plate; gold plate; ajid some chrome
plate.
(b)	Good materials, loss 0.10 to 0.16 gm. — Gun steels;
plain carbon steel; most alloy steels of the SAE, machine grade;
diffused molybdenum coating; diffused tungsten coating; and
nitriding steels.
(c.) Excellent materials, loss less than 0.05 gm. •— High
chromium (2? percent) steel; chrome plate, when made very adherent;
and diffused tantalum coating. Each of these materials, howeveir,
has some drawback to its application to gun tubes.
Some of the most recent experiments with this laboratory gun
have shown that in reality it is a form of erosion vent plug in
which the vent is annular in cross section. The movement' of the
- 163 -
projectile contributes nothing, apparently, -fco the test of a material,
for the same weight loss and heat-check pattern were obtained in an
experiment in which the projectile was held in place as in one in
which it moved. Consequently the test is being modified to employ
a vent of rectangular cross section, formed by two opposite plane
surfaces separated by a fixed distance. It is felt that this modi-
fied test will give essentially the same results as the one with
the moving projectile, with much less trouble in the preparation
of the specimen. It has been suggested, furthermore, that one face
of the vent can be formed of the material being tested and the
other of a standard material, in order to provide continuous control
of the conditions of the test [Russell, 19h-2].
89.	Pressure gages—/
In test firings of guns and in closed-chamber experiments the
pressure of the powder gases is frequently measured. The crusher
gage has long been employed for the measurement of the maximum
pressure in a gun. The piezoelectric gage, although it is more
accurate, is limited in use to special investigations, because 'a
hole has to be made into the chamber of the gun for its insertion,
and also because it is a laboratory instrument that requires special
care in its use.
(a)	Crusher gage. — A form of crusher gage was invented by
General Thomas J. Rodman of the U.S. Army, in 18^7> and then was
. > 82/ The design and response characteristics of gages suit-
able for the measurement of the stresses generated by propellants
and high explosives are discussed in detail by Goranson, Garten and
Crocker [19Ц2].
- 16Ц -
modified by Noble [187$; p. 107 in 1906 reprint] and by various
later investigators [for example, Vieille, 1906; Desmazidres,
1922; and Burlot, 1923] ♦ Such a gage usually consists of a
small metal cylinder at the bottom of a hole in a metal housing.
The cylinder is compressed by a piston that is pushed into the
hole when the pressure is applied. A gasket at the top of the
piston prevents leakage of gas into the hole. The permanent
change of length of the cylinder caused by compression is a
measure of the maximum pressure. Annealed copper§^/ has been
the metal most frequently used for the cylinders; but lead is used
in some minor-caliber gages, especially for the measurement of
pressures less than 10,000 Ib/in? (700 bars). In order to prevent
undesirable dynamic effects that would be produced if the travel
of the piston were very great, copper cylinders intended for the
measurement of pressures above h0,000 Ib/in? (2800 bars) are pre-
comprbssed within 20,000 Ib/in? (1Ц00 bars)* of the expected pres-
sure. One or more of the gages are placed in the powder chamber
at the base of the charge, after the several parts have been care-
fully cleaned and oiled. Although copper crusher gages indi-
cate pressures some 10 to 1$ percent lower than those registered
by a piezoelectric gage, their results are self-consistent, and
hence they furnish a convenient means of measuring the maximum
pressure in a gun without altering the gun itself.
83/ The maximum pressure in a gun is sometimes said to have
been measured by ’•coppers," which means by copper crusher gages,
8Ц/ Detailed directions concerning the use of these gages are
given in Ord.Dept.[1 91$]; Ord.Dept.,[1932] and Ord.Dept.[1936],
No. Ц0-16.	~
— 165 —
A recently suggested improvement to the technic of pressure
measurements with crusher gages [Hickman, 19Ш] is the use of
5/32- or 3/16-in. annealed copper balls instead of cylinders.
Because the ball presents an increasing area with increasing com-
pression, a much wider range of pressures may be covered. Further-
more, the balls of a given lot from a commercial source are so
nearly of the same diameter that it is not necessary to measure
each one of them before use. The calibration curve is essentially
a straight line throughout the range 0 to 15,000 Ib/im (0 to 1000
bars) under static load.
The use of a crusher gage in a gun slightly affects the
ballistics. Thus it was found in the firing of a 37_mm gun M1A2
that a certain charge of powder would produce a velocity of
2600 ft/sec with the gages in the gun, whereas the velocity was
I
5o to 60 ft/sec lower when this charge was fired without the gages
[Ord. Dept., 19Ц1]. , This result is naturally to be expected,
because the removal of the gages decreased the density of loading.
(b)	Piezoelectric gages. —A piezoelectric pressure gage
consists of several crystals of quartz or tourmaline so arranged
that when they are compressed, the charges of electricity that are
developed on opposite faces of each crystal are added together.
This total charge is very small; the piezoelectric constant for '
quartz at room temperature, for instance, is -6.90 (esu/cm2)/(dyne/cm2)
[International Critical Tables, vol. 6, p. 209]; hence a pressure
of 1 kilobar produces a charge of 1 microcoulomb when exerted on a
— 166 -
total surface of approximately 100 cm? The charge is a linear
function of the pressure above a certain limiting pressure.
The piezoelectric gage originally devised by Sir J. J.
Thomson [1919; also Keys,1921 ] for measuring explosion pres-
sures used tourmaline crystals, the charge on which was measured
by means of a cathode-ray oscillograph. The gage that has been
developed at Aberdeen Proving Ground especially for the measure-
ment of powder pressures [Kent, 1927] contains a stack of quartz
plates. At first the charge was measured by recording the deflec-
tion of a ballistic galvanometer on moving film [Karcher, 1922];
but later measurement was made by amplifying the charge with a
vacuum-tube amplifier and then recording it with a General Electric
Company oscillograph and the high-speed spiraling-drum camera des-
cribed by Eckhardt [1922]. In its present form [Kent, 1938b] this
gage is connected through a vacuum-tube amplifier to a cathode-ray
oscillograph having a fluorescent screen that is photographed by
an external camera. It can be used as far away from the gun as
half a mile [Kent and Hodge, 1939].
The especial merit of the piezoelectric gage is that it is
capable of recording rapidly fluctuating pressures, because the
response of an oscillograph, especially a cathode-ray oscillograph,
is so nearly instantaneous. Another important advantage is that by
a proper choice of electric circuits, it is possible to obtain
directly the time derivative of the pressure as a function of either
the time or the pressure (see Sec. 31, Part I).
- 16? -
(с)	Other pressure gages. — The spring manometer developed
by Peteval [190$; also Bone, Newitt and Townsend, 1929, pp. 93-96]
is slightly more accurate than a piezoelectric gage, but it is not
suitable for use in a gun because its action is affected by the
recoil. It has been used extensively in closed-chamber experiments.
Another form of mechanical pressure gage that can be used in
a gun has been developed at the Naval Proving Ground, Dahlgren,
Virginia [Webster and Thompson, 1919]» It consists of a stiff
metal girder so mounted that the slight distortion caused by the
pressure of the powder gases moves a contact on a variable electric
resistor. The resulting change in resistance, and hence the motion
of the girder, is recorded by having the resistance form part of a
bridge circuit. Although this gage is not as sensitive as a piezo-
electric gage, it is much more rugged.
The diaphragm pressure gage has been used for the measure-
ment of explosion pressures amounting to a few hundred pounds per
square inch, but it does not seem to have been used for measuring .
pressures as high as those in a gun [Bone, Hewitt and Townsend,
1 929, pp. 99-WO; Caldwell and Fiock, 19hl ].
A recent development is the use of a strain gagq for the
measurement of powder pressures, such as the one described by DuMond
[19Ul] for measuring and recording the pressure of powder gases in
rocket chambers.
- 168 -
CHAPTER XI. RELATION BETWEEN PROPERTIES OF
THE GUN METAL Al© EROSION
90.	Composition and physical properties of the gun metal
Various alloy steels have been used for gun barrels and tubes;
but a quantitative comparison of the rates of erosion cannot be
obtained from the ordinary service records because the guns are not
fired under the same conditions. The normal variations in the rate
of fire, in the amount and kind of powder, and in other conditions
introduce variations of about + £0 percent in the average life of a
gun of a given model. Within these limits the variations in the
properties of the gun steel do not seem to affect the rate of
erosion.
91.	Nickel steel
Kosting, in his review of erosion [193h], had suggested that
steels containing a high percentage of nickel erode more rapidly
than some other alloy steels. His conclusion was based on a com-
parative firing at Aberdeen Proving Ground [Lane, 1933] of two
radially expanded 3~in. antiaircraft-gun tubes, one of nickel
steel (C, 0.U5 percent; Mn, 0.7h percent; Si, 0.2Ц5 percent;
Ni, 2.Ц1 percent; Cr, 0.13 percent) and one of carbon steel (C,
0.Ц1 percent; Si, 0.217 percent; Mn, 0.65 percent). After 2000
rounds the increase in diameter across the lands was 0.208 in.
for the nickel-steel tube and 0.170 in. for the carbon-steel tube
at the origin of rifling and 0.02Ц in. and 0.002 in., respectively,
at the muzzle. The loss of muzzle velocity, however, was about
- 169 -
1^0 ft/sec for both. guns. In a letter to Datertown Arsenal comment-
ing on this report, Rear Admiral Defrees said that Kosting*s con-
clusion whs substantiated by the experience of the U.S. Naval Gun
Factory.
92.	Special alloy steels in machine-gun barrels
One of the most extensive series of tests of steels for gun
barrels was that conducted jointly by the Springfield Armory and
the National Bureau of Standards during the five-year period from
1919 t-o '192Ц, on the effect of chemical composition and other
factors on the erosion of Browning caliber f30 machine-gun barrels.
Ovep 20 separate reports and memoranda were issued from time to
time. Fortunately, a comprehensive report [Bur. Stand., 192ЦЬ]
summarizes the results and gives complete references to the indi-
vidual reports, some of which contain more details.
The compositions of the steels that were tested are listed in
Table XXII (A). —For steel of each composition, five full-length
barrel blanks were rolled from a i|-in. square ingot that had been
made by the crucible process by the Bethlehem Steel Company. The
thermal expansion to 900°C and the critical temperatures, which were
determined by the method of thermal analysis, were measured at the
National Bureau of Standards [see Table XXII (B)], after which
a heat-treatment was planned to develop a limit of proportionality
85/ These compositions were chosen by G. K. Burgess, then
chief of the Metallurgical Division of the National Bureau of
Standards, after consultation with representatives of the Tech-
nical Staff of the Ordnance Department, U.S, Army, and with other
persons interested in the projectJ
- 170 -
Table XXII. Properties of special steels tested for
Brov.-ning machine-gun barrels.
(A) Chemical composition (weight percentage).
Barrel . No.	c	Mn	Cr	V	p	S	Si	Other
0	o.hh	0.69			0.011	0.017	0.21	
1	.h3	1.22	——	——	.0h6	.0h9	.12	
2	.38	O.67	——	—	.0h6	.055	.07	
3	.ho	.55	— 	0.15	.006	.031	• 13	
li	.55	.92	—	—	.020	.026	.26	
5	0.32'	0.11	1.20	0.11	0.005	0.028	0.12	
6	.27	.hh	0.69	.ih	.005	.031	.09	
7	.10	.008	2.5h	.hi	.005	.033	.12	Ni h.5
8	.21	.77	—	——	.058	.09h	.05	Ni O.h9
9	,16	.08	1.1h	.21	.016	• 0h7	.11	Cu 1.88
10	0.22	0.075	——		0,008	0.028	0.02	
11	• 1h	.060	0.93	0.25	.009	.017	.13	Mo 0.60
12	.05	.030	1.38	.21	.011	.019	.91	
13	.29	.81	—	——	.013	.038	.09	Ni 3.71
ih	• 35	1 .h5	1.11	J3	.012	.056	.20	
15	0.32	0.28	0.80	0.28	0.017	o.oh6	0.15	Cu 2.76
16	.33	.26			.009	.057	.°5	W 3.82
17	.36	1.21	—	—-	.053	.077	.09	Ni 0.81
18	.ho	1.30	—		.011	.060	1.10	Ni 3.70
19	.50	0.39	—	—	.009	.013	0.17	W 1.59
20	0.25	o.ho	13.98		0.006	0.010	0.77	
22	.32	.66	——	—	.023	.028	.37	U 0.22
23	.19	1.05		——	.022	.031	. 16	Ni 36.33
- 171 -
Table XXII. (Continued.)
(В.) Thermal properties.
Barrel ' No.'	Average expansion coefficient, x 10°			Critical .1	'emperatures
	25° to 300°C	300° to 6oo°c	600° t0 900°C	. Acx Max. (°C)	Arx Max. (°C)
Manganese					
0	12.1	16.2	16.8	(a)	(a)
1	12.7	16.5	16.7	72Ц	65o
2	12.7	15.8	16.6	(a)	(a)
3	12.7	16.1	16.8	7b9	680
h	12.9	16.1	16.6	73h	666
10	12.5	16.0	16.9	U)	(a)
Manganese, chromium, vanad: 	 	 	 								.um	
$	12.9	16,0	16.2	76h	718
6	13.1	15,9	16.8	750	692
11	12.5	.15.9	16.1	—	—
12	12.7	15.2	15.8	801	735
1h	13.3	15,6	16.2	753	659
		Manganese, nickel			-
7	12.1	1Ц.З	———	(b)	(b)
8	12.6	16.1	16.Ц	731	670
13	12.1	15.3	———	' (a)	(a)
' 17	12.9	16.1	* 16.Ц	(a)	(a)
18	. 12.3	- 15.0			716	.	
	Manganese, chromium, vanadium.			copper	
9	12.7	15.7	16.7	771	688
15	12.9	16.1	16.9	759	682
Tungsten, manganese					
16	12.5	15.7	16.5	7U1	681
19	12.2	15.9	———	7U0	680
Chromium (stainless)					
20	11.0	13.3	13.7 •	——	—
(a	I No thermal	miWe taken.			
(b	i No definite	transformation.		-	
- 172 -
Table XXII. (Continued.)
(C) Heat treatment and tenaile properties.
Barrel No.	Temperature(°F)		Brinell Hard- ness	Tensile Strength (lb/in?)	Prop. Limit (lb/in?)	т	 Elonga- tion (percent)	Reduction in Area of Cross Section (percent)
	Quencha	Temper13					
Manganese
0	1600-0	900-N	2Ц1	12h,65O	75,000	20	Ц6
1	i5oo-o	1250-F	2hh	1ih,65o	85,000	23	59
2	1600-0	950-N	228	112,800	70,000	20	Ц6
3	1575-w	1200-F	217	103,100	80,000	26	65
Ц	1500-0	1250-F	223	110,750	67,000	2Ц	58
10	1650-w	500-0	177	81,100	55,000	25	6Ц
		Manganese,		chromium,	vanadium		
5	1600-W	1200-F	196	96,200	60,000	26'	65
6	1600-W	1250-F	196	95,100	73,000	26	69
11	1650-w	1325-F	286	12h,050	105,000	23	66
12	175o-w	500-0	235	110,000	53,000	19	Ц2
111	1625-0	1250-F	2h1	115,600	100,000	23	58
Manganese, nickel
7	1650-w	11 75-f	2Ц2	118,100	80,000	20	66
8 .	1550-w	700-N	185	90,Ц00	63,000	28	68
13	ili75-o	1125-F	235	112,300	92,000	26	66
17	1525-0	900-N	225	113,500	90,000	2h	5U
18	1600-0	1150-F	277	1U2,5OO	65,000	27	Ц6
Manganese, chromium, vanadium, copper
9	1650-w	1300-F	235	108,100	98,1iOO	23 '	6Ц
15	1650-w	1125-F	2li1	1O7,U5O	70,000	21i	66
Tungsten
16 19	1550-W 1550-w	1100-F 1250-F	2Ц1 2Ц8	9h,500 1 oh,85o	70,000 90,000	28 29	61 56
Chromium (stainless)							
20	1800-0	125o-fc	269	120,600	75,000	22	60
Nickel (invar							
23	. None	None	1h9	9h,000	6t,25o	33	63
a0, oil; W, water.
bp, open flame; N, nitrate bath; 0, oil.
cHeat-treated after machining.
- 173 -
Table XXIII. Firingtests of Browning machine-gun barrels made of special steels.
First. Test			Second Test					
No.	Accuracy Life ... (rds)	Condition	No.	Order of Accuracy			Muzzle Velocity	
				2000 rds	6000 rds	7000 rds	Initial (ft/sec)	Loss, 6000 rds (percent)
Manganese
0 1	6000 8000	Bulged Bulged	1B 1C	8 8	* 7	J	2618 2622	li.Oh 3.05
2	8000	Bulged	2B	1	#	—	265U	5.06
			2C	3	*	-	26ЦО	3.30
3	10000		3B	6	*	—	2655	3.1U
			30	1	11	6	26hU	U.3U
U	7000	Bulged	1»B	5	*	—	2618	2.93
			UC	5	*	-	2616	3.60
10	2317						1	
Manganese, chromium, vanadium
5	9000	Bulged	5b	9	5	—	2612	2.75
			5c	u	6	1	2629	2.62
6	6000	Bulged	6B	13	7	, -	2623	3.16
11	UOOO	Bent						
12	8000		12B	11	2	—	2601	1.97
			12C	6	10	-	2660	3.31
Manganese, nickel
7	8000							
8	8000		8B	2	10	—	2635	3.32
			8C	10	13	-	2665	U.70
13	9000		13B	10	8	- —	2605	2.10
			13C.	7	12	-	2613	: 1.61l
17	8000		17B	7	3	—	2612	3.95
			17C	2	5	Il	2622	3.00
		Manganese, chromium			vanadium,	copper	-	
9	8000		9B	12	2		2668	5.19
			9C	9	8	-	2665	. Л.62
15	1705	Bulged						
Tungsten, manganese ,								
16	8000		16B	15	.11	- -	2620	2.71
19	9000		19B	3	1	—	2609	2.53
			19C	11	U	2	26Ц0	2.65
Chromium (stainless)								
20	Barrels spoiled in		20B	1U	12	1	2632	3.18
	machining operations		20C	9	2	5	26U3	5.15
Uranium
22		22B 22C	U 6	13 9	3	2620 2631	2.79 2.70
* Not rated.
- 17h -
of at. least 75>,OOO lb/in>, coupled with a minimum elongation of
20 percent in a 2-in. gage length. After some trial quenchings,
each group of barrel blanks was given.the heat-treatment best
adapted to it, and then the microstructure was examined. The heat-
treatment and resulting thermal properties of each steel are listed
in Table XXIl(C).
One barrel was made from each group of blanks and fired for
erosion at Springfield Armory. The rate of fire was not stated,
except that 5>0-round bursts were used for the targets. All barrels
were fired 11,000 rounds regardless of their accuracy life, except
for several barrels that became unserviceable because of bulging.
The end of life of the barrels, which is. listed in the second column
of Table XXIII, was taken as the point at which keyholing (Sec. 82)
occurred on a screen 100 ft from the muzzle. •
Two more barrels were made up from each of most of the re-
maining, original ingots. These barrels were fired for erosion,
and the accuracy was measured after each 2000 rounds. The order
of accuracy that is listed in columns p, 6 and 7 of Table XXIII
was determined by the relative degree of clustering of the shots.
It should be noted that the order after 6000 rounds was consider-
ably different from that after 2000 rounds. Part of the reason for
this variation was the smallness of the differences among the various
barrels, but part of it also reflects the general order of uncertainty
of such a test. As mentioned by Hatcher [ 1920a], ''experience with
service machine-gun barrels has shown that several barrels of
identical heat-treatment and material will vary in accuracy life
from I4.OOO to 8000 rounds."
. -175- .
The conclusions [Bur<Stand. ,1 92lib] were.as.followb:
It is very evident from the. results obtained that there
are noticeable differences in the behavior of. the different
barrels. 'Just how much is to be attributed to the different
variables in composition is somewhat problematical. The
results available are .entirely too few to permit any very
/ definite or wide-sweeping.conclusions being drawn. The wide
discrepancies found in some cases for barrels of the same
steel in the two firing tests or even between two barrels of
the same steel in the second firing series emphasizes this
fact.
In ranking the barrels with respect to erosion, it is
most convenient to compare them with barrel No. 1 [the nominal,
composition of which was essentially that of the "standard1*
used for machine gun barrels]'. Of the barrels tested, Nos. 22,
20,	3 and 17 are superior to the "standard barrel," the
first two being distinctly so. They all showed less wear on
the lands and grooves at the breech section of the bore. For
many of the others, including, the "standard," the rifling
was completely worn away for a distance of several inches at
the breech end wdth a considerably smaller number of rounds
fired. In accuracy all the barrels listed above surpassed
the standard, the comparison being based upon the order in
the arrangement of the targets. The depth of penetration of
the erosion cracks was also considerably less in most cases
and the decrease in velocity noticeably less. In this respect,
the conclusions expressed here are not in complete agreement
wdth that reached in the final report from the Springfield
Armory which was to the effect that "none of these barrels
have shown any marked improvement over the regular service
barrel in regard to accuracy life." The magnitude of the
difference between these conclusions depends, of course, upon
how "marked" the improvement must be in order to receive
recognition.
While it is evident from the tests that superiority of
the different steels over the standard is associated with
differences in composition, no definite statements can be
made upon this point. However, concerning tho correlation
of "erosion11 and mechanical properties, it appears from the.
results available for comparison that erosion resistance
cannot be predicted, a priori, by a determination of the
mechanical properties, at least as carried out ordinarily at
room temperatures. By way of example, steel No. 5 (chromium-
vanadium), which is here ranked as superior to the "standard,"
showed in the mechanical tests a proportional limit of only
60,000 and an. ultimate tensile strength of 96,200 lb/in?,
whereas another chromium-vanadium steel No. 9 (containing
copper), which did not show superiority to any extent in the
firing tests, had a proportional limit of 9В,Ц00 and an
ultimate tensile strength of 108,100 lb/in?, the ductility
- 1?6 -
in the two cases being not materially different (No. 5,
elongation, 2 in. or 26 percent, reduction of area, 6$ per-
cent; No. 9, 22.5 and 63.5 percent, respectively).
The malfunctioning of a gun on account of bulging or
similar causes appears to be more closely related to the
mechanical properties of the steel than is the erosion
resistance. Although bulging was not experienced with
all the steels having the lower tensile properties, the
cases which did occur were confined, for the greater part,
to such steels. However, it should be borne in mind that
the results of these tests indicate that one cannot pre-
dict with any degree of assurance the malfunctioning of a
gun by reason of bulging or similar causes on the basis
of the low tensile properties of the steel.
Three barrels that were made of invar steel were tested as a
supplement to the Springfield firings just described. They have
been listed as No. 23 in Table XXII(A), The metal was so tough
that drilling was difficult [Ames, 1921]. The three barrels were
fired until pronounced keyholing of the target occurred at 100 ft.
The numbers of rounds fired were: barrel No. 1, 3500; No. 2, 17ОО;
No. Ц000. The lands were entirely removed for a distance of 6
to 12 in. from the origin of rifling [Hatcher, 1920b]♦
In addition to the conclusions already quoted, it was sug-
gested [Bur. Stand., 192hb] that the steels that had superior
erosion resistance showed very small permanent dimensional changes
as a result of thermal transformation. It was admitted, however,
that not all steels which showed small change were erosion re-
sistant.
93.	Nonferrous metals used for gun barrels
Metals other than steel that have been tried for machine-gun
barrels have included beryllium-copper, monel and molybdenum. The
- 177 -
barrels of beryllium-copper, which were tested at Springfield Armory
oz /
about 1938, had extremely short lives.—'
The U.S. Navy has tried some, monel-metal guns in an effort to
g У /
reduce sea-water corrosion. The erosion— of a 3-in./5O-caliber
unplated monel gun (No. 5533) was 0.06l in. at the origin after
z,	88/
6Ц1 E.S.R.,— which was about the same as that of a standard
3-in./5O-caliber Mk. 20, unplated steel gun (No. 2956) firing the
same ammunition at a muzzle velocity of 2700 ft/sec. After 1255
E.S.R. the erosion of the monel gun had increased to 0.085 in.
A molybdenum liner was tested in a caliber .30 machine gun
at Aberdeen Proving Ground in 1936 [Lane, 1936]. The liner, which
was 6 in. long, was shrunk into a caliber .30 barrel blank and then
bored, chambered and rifled. Because the liner was pushed back-
wards by the powder gases while the bullet was in the forward part
of the barrel, the barrel had to be cut off -jj in. in front of the
liner. For comparison a standard М2 barrel was similarly altered.
Each barrel was fired Ц6Ц9 rounds at-such a rate that a thermo-
couple placed on the barrel registered a temperature of 900°C.
Although the molybdenum liner did not have a homogeneous structure
and had not had a smooth inner surface because of difficulty in
machining it, the lands of this liner eroded less than those of
the steel barrel — 0.007 in. and 0.011 in., respectively, after
86/ Capt. С. E. Balleisen, U.S. Army, personal communication.
87/ Lt. В. B. Mills, U.S. Navy, personal communication.
88/ Equivalent service rounds; see Sec. 12Ц.
- 178 -
Ц000 rounds — and the grooves did not erode at all. Microscopic
examination of a longitudinal sectipn of the molybdenum liner
showed that there were no heat checks in front of the chamber,
•whereas the standard steel barrel had the customary heat checks.
These results were considered to support the gas-washing theory
of erosion advocated by Greaves, Abram and Rees [1929], the ero-
sion of the lands having been ascribed to the abrasion of the
bullet and the lack of erosion of the grooves having been ex-
plained by the high melting point of molybdenum (2бОО°С).
9h. Erosion vent plug tests
(a)	Pure metals. — Other investigations of the erosion
resistance of metals have been made by means of erosion vent
plugs. Vielle [1901], for instance, measured the erosion of a
number of pure metals and alloys in the form of vent plugs fitted
to a closed chamber that had a volume of 17-8 cm3 and in which was
fired a charge of 3.55 gm of ballistite containing 50 percent nitro-
glycerin. Vieille claimed that for pure metals the erosion in-
creases in inverse proportion to the melting temperature. This con-
clusion is only partially substantiated by the data that he gave,
which is reproduced in Table XXIV. In terms of volume, which was
the basis of comparison that Vieille used, zinc eroded less than
aluminum, and one sample of copper eroded less than iron or
platinum.
(b)	Alloy steels (U.S. Army). — The effect of alloying
elements on the erosion resistance of steel was investigated by
Ritchie [ 192 8] by means of erosion vent plugs. He made up a series
- 179 -
Table XXIV. Erosion of pure metals as a function of melting
point.'
Metal	Melting Pointa(CC)	Specific Gravity^1	Erosion0	
			Volume (mm3)	Mass (gm)
Platinum	1755	21.5	59	1.27
Iron	1535	7.8	68	0.53
Copper	1083	8.9	998	.88
Silver	960	10.53	231	2.U5
Aluminum	660	2.60	2238	• 5.82
Zinc	Li19	7.15	1018	7.28
*After Vieille [1901].
aThe melting point given is that listed in the International
Critical Tables. The values given by Vieille had differed somewhat
from them.
^The specific gravity is that given by Vieille, which does not
differ much from current values.
cThe mass of metal eroded has been computed for this table from
the volume eroded and the specific gravity given by Vieille.
d-The value given is the mean of two for "red copper for crusher-
gage cylinders." Vieille also listed four values for commercial red .
copper, ranging from Ц8.7 mm3 (O.h3 gm) to 90.8 mm3 (0.8l gm). This
wide variation was perhaps due to" impurities.
of Ц1 alloy steels and subjected them to the following tests: , (i)
proportional limit, (ii) tensile strength, (iii) elongation, (iv) re-
duction, (v) Charpy impact. These tests were conducted at 7O0, 600°
and 1000°F on annealed and heat-treated specimens and also at 70°F
on both annealed and heat-treated specimens (a) after cold-working
and (b) after cold-working followed by soaking at h80°F. The cold-
working was obtained by cold-drawing to a 6-percent increase in
length. Photomicrographs were taken of all specimens, both annealed
and heat-treated. The two steels which had the most all-round
- 180 -
desirable physical properties were one containing 0.25-0.30 per-
cent C, 1.25 percent Mn and 0.35 percent Mo, and another contain-
ing 0.25-0.30 percent С, 1.50 percent Mn, 0.35 percent Mo and
0.075 percent Zr.
Specimens of the annealed and heat-treated bars (not cold-
worked) in tho form of vont plugs were tested for erosion at
Aberdeen Proving Ground [Kent, 1926]. Each erosion test bar,
which weighed 19.Ц oz, had a vent 0.156 in. in diameter. It was
fitted to a closed chamber having a volume of 1000 cm3, which had
been constructed from a 5-in. gun. A charge of 7 lb l5 oz of
powder was fired, all the gas from which escaped through the vent
in slightly over sec. After erosion the hole ranged in diameter
at the breech end from-0.35 to 0.53 in. and at the muzzle end from
0.32 to О.ЦЦ in. The enlargement at the breech end was always
.the greater. The maximum, minimum and average losses in weight
for the three classes of steel—are given in Table XXV(A). Each
chrome or chrome-vanadium steel was tested in both the annealed
and the heat-treated conditions; and the same was true of all but
three of the manganese steels. Three of the stainless steels
were annealed, the fourth was heat-treated.
89/ P. R. Kosting (personal communication, Aug. 22, 19112)
has suggested that "the data collected by the Army by means of
the erosion -vent plug can be divided into two subgroups; one of
low-alloy steel and the other of high-alloy steel, such as 12 per-
cent Or stainless alloy. Yihen sensitivity and reproducibility
of the results are taken into consideration it is believed that
Greaves, Abram and Rees* conclusions that low-alloy steels have
the same erosion rate in vent plugs will be substantiated.”
f
- 181 -
Table XXV(A). Loss of weight of erosion vent plugs.
Type of Steel	No. of Specimensa	Loss in Weight (percent)		
		Max.	Min.	Avg.
Manganese	5i (27)	30.7	20.8	27.3
Chrome and Gr-V	22 (11)	Ц3.1	21.7	28.9
Stainless 12 percent Or, 0.Ц percent Ni	h (Ц) _	5	36.2	38.2
*After Ritchie [ 1 92 8 ].
aThe number in parentheses indicates the number of different
compositions of each type of steel, some of which were tested in
duplicate.
It wafe observed that heat-treatment seemed to have little effect
on erosion, and' that '*the apparent average depth of change in struc-
ture from the bore outward on the manganese steels was 0.031 in. as
against 0.025 in. for the chrome and chrome-vanadium steels. In
other words the depth effect on the manganese steels is greater while
at the same time they suffer slightly less erosion than do the other
steels"[Ritchie, 1 928] (see Sec. 73)-
(с.) A^°y steels (U.S, Navy). — The Naval Proving Ground has
also tested a large number of erosion vent plugs. A summary'[Bur.
Ord., 1931] of one series of these tests was enlarged [Bur. Ord.,
1938a] to include subsequent results. Each plug-was tested by
fitting it in the. base of a 12-in. armor-piercing projectile, volume
2h9 in? and firing a charge' of 2.25 lb of pyro powder through its
orifice, .after which the loss of weight was measured. The wires
attached to the electric primer ("squib") that was used to set off
- 182 -
the powder passed through the hole in the plug, the diameter of
which was not stated. The tungsten steels, nitralloys, stainless
steels and monel were all inferior to gun steels, as is shown in
Table XXV(B). Both the plain carbon and the nickel gun steels
Table XXV(B). Loss of weight of erosion vent plugs.
Type	No.	Loss of Weight (percent)
Gun steels, chrome plateda	10	9.7 “ 11-7
Gun steels, unplateda	38	10.1 - 12.3
Tungsten steels (0.6, 1.1, and 2.3 per- cent w)-	3	11.8 - 12.5
Nitralloys, nitrided	h	12.6 - 13.1+
Stainless steels (12.2 to 20.6 per- cent Cr)	7	13.1 - 16.Ц
Inconel (79.6 percent Ni, 13.5 percent Cr, 5‘. 7 percent Fe)	1	13.7
Konel (66.9 percent Ni, 1.Ц percent Fe)	1	20.0
К-Konel (6^.6 percent Ni, 3«5 per- cent, Al, 29.1 percent Cu, 1.3 per- cent Fe)	1	22.3
"'^After Bur. Ord. [193da]
aGun steels include carbon steels, nickel steels (2.2 to
3.3 percent Ni) and low alloy steels containing 1 percent or less
of Ni, Cr, V and Lio.
that were chrome plated eroded less than the unplated plugs of the
same steel; and in both cases the least loss was suffered by the
plug plated with the thinnest coating (0.0005 in.)
95.	Effect of structure of steel on erosion
The structure of the steel may also affect its erosion re-
sistance. Rockwell [1919], for instance, suggested that slag in
- 183 -
the steel nay accelerate erosion. Photomicrographs made by Kosting
[19й0] support this conclusion (see Sec. 78). Kosting [193h, p. 11
also suggested that in guns, ’’steels of uniform sorbitic micro-
structure with absence of much free ferrite tend to have longer life
than steel not treated for uniformity of structure.”
96.	Effect of radial expansion (cold-working) on erosion
The effect of radial expansion on the erosion of a nickel-steel
gun was investigated in the case of a 3_in. gun [No. 1(B-1)] that
was compared with a built-up gun (No. 91). After having summarized
the results, Lane [1933] concluded that the radially expanded gun
was superior to the built-up gun; but the reason fbr this conclusion
was not stated except by reference to the curves showing the enlarge-
ment of the bore as a function of the number of rounds. These curves,
however, do not substantiate the conclusion, for the enlargement at
the origin after 2000 rounds was 0.15 in. on the lands and 0.08 in.
in the grooves for the built-up guns, whereas it was 0.21 and 0.15 in.,
respectively, on lands and grooves of the radially expanded gun.
The star-gage records show also that after 2000 rounds the lands
of the radially expanded gun had been enlarged 0.02Ц in. at the
muzzle, whereas those of the built-up gun had been enlarged 0.011; in.
On the other hand, the accuracy life of the radially expanded gun
was 10 percent greater than that of the built-up gun — 2220 rounds
instead of 1990 — and the loss of muzzle velocity was only 95 ft/sec
for the radially expanded gun after 2000 rounds compared with
165 ft/sec for the built-up gun. Also the mean deviations in
velocity, were somewhat less and much more regular for the radially
- 18Ц -
expanded gun than for the built-up one. The comparison was com-
plicated by the fact that several different kinds of projectile
were used in the firings of the built-up gun. Also the gun steels,
made by different manufacturers, were different in chemical com-
position and heat treatment. All in all, therefore, the comparison
was inconclusive.
97.	Effect of condition of bore surface on erosion
The nature of the surface of the bore in a mechanical sense
may also influence erosion. Thus both Fleming [1919] and de
Sveshnikoff [1922] considered that tool marks represent ’’incipient
erosion,” for the reason that the powder gases would be expected
to react more quickly with a roughened surface than with a smooth
one. Also recent researches in connection with such processes as
Chrysler's "Super-finish” have shown that the deformation of the
surface of steel during finishing varies with the type or process
used [Wulff, 19Ul ]; therefore it might be expected that the sur-
face of a gun bore finished by machining would have been deformed
more than one finished by a less drastic process, and would con-
sequently be more reactive to the powder gases. The bores of
90/
some guns are now being honed,—• but records are not yet avail-
able to show whether such a surface resists erosion any better
than the usual machined surface. If any improvement did occur
it would only apply to the lands, because the grooves are cut after
the honing operation.
90/ Personal observation, Watervliet Arsenal, 19Ц1.
- 185 -
98.	Chrome-plat ed. Navy guns
Since the middle thirties U.S. Navy guns have been chrome
plated to protect them against sea-water corrosion. After such
plated guns had been in use, it was discovered that they eroded
less than unplated guns fired under the same conditions — especially
at the muzzle. A quantitative comparison of a plated gun with un-
I
plated guns was made during the.experimental firing of 1 Ц-in./50-cali-
ber guns in 1938. Gun No. 110L2, Mark C, was fired 207 equivalent
service rounds during 209 actual rounds, which was somewhat beyond
the end of effective life.
The behavior of the chrome plating was markedly different at
the two ends of the gun. At the muzzle,
91 /
... flaking was first noticed at 52 E.S.R.— but no
appreciable amount of plating was gone until 62 E.S.R.,
when plating had worn rapidly on top of the lands (60 per-. .
cent gone for 5 ft at 62 E.S.R.) so that at 73 E.S.R. plating
was gone from on top of the lands for 6 ft aft. From then on
the plating wore off farther aft slowly until at 12Ц E.S.R.
it wras worn off for 18 ft aft of the muzzle. Wear on the
side of the lands and in the grooves was first noticed at
83 E.S.R. Q5__p_ercent gone), but wear here was slow and at
12Ц E.S.R. amounted only to 30 percent for 18 ft aft (wear
on driving sides being greatest). [Bur. Ord,, 1938b, par.11,]
At the breech end, on the other hand, erosion was scarcely affect-
ed by the chromium plating.
The plating on the slope of the origin was gone after
15 E.S.R.; the plating from the origin to 18 in. forward of the
origin wore rapidly and at 36 E.S.R..was 65 percent gone.
At Ц.1 E.S.R. the plating at the origin was all gone, de-
creasing to 55 percent gone Ц ft forward, then to 1 percent
gone 8 ft forward. The plating then wore with regularity
to 73 E.S.R., when it was 90 percent gone 6 ft forward.,
. 91/ Equivalent service rounds; see Sec. 12Ц for method of com-
putation.
- 186 -
decreasing to 1 percent gone 9 ft forward. From then on
the wear was slow until at 12Ц E.S.R. the plating was
90 percent gone 8 ft forward and 1 percent gone 11 ft
forward. [Bur. Ord., 1938b, par. 11.]
In the intermediate section of the gun, from 11 ft forward
of the origin to 18 ft aft of the muzzle, a distance of 21g ft, the
plating appeared intact at 12Ц E.S.R, [Bur. Ord., 1938b, par. 11].
The life of a 1 Ц-in./ЗО-caliber gun was considered as the
number of rounds at which enlargement at the origin, AD, reached
0.Ц in,, or enlargement at the muzzle, AM, reached 0.1 in., or at
which [Bur. Ord., 1939a, par. 6]
Z [ x i ( AD/O. Ц j + |(AM/0.1)]'- 1.
Inasmuch as AM reaches 0.1 in. before AD reaches 0.Ц in. in un-
plated ЛЦ-in, guns, the end of life is caused by muzzle erosion.
Therefore the retardation of muzzle erosion by chrome plating
increased the life of gun No. 110L2 about Ц0 equivalent service
rounds, from 113 to 133 E.S.R. [Bur. Ord., 1939a, par. ЦЬ]. The
enlargement at the origin of chrome-plated gun No. 110L2 after
207 E.S.R. was О.О38 in. more than the average for unplated guns;
but inasmuch as the total enlargement amounted to only 0.3h8 in.,
it was not enough to decrease the life of the gun [Bur. Ord.,
1939a, encl. 0]. A slight decrease in the loss of velocity of
chrome-plated gun No. 110L2 up to 80 E.S.R. was attributed to
decreased erosion forward of the origin of rifling [Bur. Ord.,
1939a, par. Це]. This decrease was manifest at first, but then
the rate of erosion at a point 1 in. forward of the origin increased
- 18? -
with respect to the rate for unplated guns, so that at about 130
E.S.R. the total erosion at this point -was the same as for unplated
guns, and after 207 E.S.R. it -was 0.028 in, greater.
99.	Experimental chrome-plated Army guns
The interest of the Ordnance Department of the Army in chrome
92/
plating—' -was originally directed toward small arms. The first
experiments with chrome-plated rifle barrels at Frankford Arsenal
in 1927-’28 indicated that a 5>0-percent increase in accuracy life
was obtained, but that the process cost Ц0 percent of the price of
a new barrel. More extensive tests of rifle, pistol and caliber .30
machine guns confirmed the conclusion '‘that chromium plating very
materially increases the resistance of small bores to both erosion
and corrosion.’* [Ord. Dept., 1929» 1 As a result of subsequent
erosion tests of caliber .30 plated machine-gun barrels at Springfield
Armory, it was reported that plating had doubled the life [Whelen,
1930].
A microscopic examination at Watertown Arsenal [Lester, 1929c]
of two of the rifle barrels plated at Frankford Arsenal showed that
the plating adhered strongly, and ’'was found on the most eroded
sections even after the firing tests.” However, it was observed
that some particles of chromium torn from the plating, had been
driven into the softer base metal,- which may have accounted for the
presence of the chromium in the heavily eroded sections.
92/ A resume of this subject, including extracts from the
original reports, was prepared by Vincent [19371» His report was
the source of the information in Sec. 99 unless otherwise credited,
i
- 188 -
During antiaircraft firings in the fall of 1928, two chrome-
plated 37-ШП1 Browning automatic guns Ml and two chrome-plated liners
for 3~in. AA guns M1 were tested. The plating, which was 0.000!? in.
thick in the 3-in. liners and of unknown thickness in the 37-mm guns,
began to flake off after a few rounds. No difference was observed in
the increase of diameter at the origin of rifling of these guns com-
pared with unplated ones; but in neither case did erosion extend as
far. forward in the plated as in the unplated guns. It was recommended
that plated guns be retested after the technic of plating had been
improved,
The guns subsequently tested comprised a 3~in. liner plated to
a thickness of 0.001 in., fired in 1929> and four 3_in. liners plated
to thicknesses of 0.001!?, 0.0020 (2), and 0.0030 in., fired in 1930.
The plating also flaked off the surface of these guns, but not as
quickly as from the earlier ones. It was again observed in the plated
guns that, although erosion at the origin of rifling was not affected
very much, the forward extent of erosion was markedly decreased. Be-
cause none of these guns was fired to the end of life, the effect on
accuracy life is not known. It was observed further that the thicker
coatings seemed less satisfactory than the thin one. Exact comparison
of the plated and unplated guns was not possible, because the star-
gaging was not done systematically.
The next trial of a .chrome-plated gun was that of liner
No. 138 for a 3_in. AA gun М3» in 1936. This liner, after having
been machined at Watervliet Arsenal, was chrome plated to a thick-
ness of approximately 0.000!?' in. at the Naval Gun Factory according
to the standard procedure used there.
- 189 -
The gun- was fired in conjunction with tests of pressure
gages. Star-gage records were made frequently. The first evidence
of erosion was noted after 2Ц7 rounds, at which time the diameter
of the lands had increased ;0.002 in. at the origin of rifling. By
the time the gun had been fired 6Ц0 rounds the increase in diameter
of the lands at the origin amounted to 0.060 in., and the increase
across the grooves was 0.019 in. (In the other chrome-plated 3“in.
liners tested in 1929-30 the increase in diameter at the origin had
been only 0.03 to 0.0Ц in.' at 700 rounds.) The eroded region
extended about $ in. forward of the origin. Beyond that point- the
chromium plating remained intact.
Measurements of muzzle velocity and of pressure made at inter-
vals with a standard charge showed a steady decrease. By round 677
the muzzle velocity had changed from the original value of 28j?O ft/sec
to 27U3 ft/sec and the pressure had dropped from about 35>jOOO lb/in?
to 31,600 lb/in? In view of these changes, according to Vincent
[1937, p.36], "it was decided that the cost of chromium-plating
liners was not warranted inasmuch as incre sjd accuracy life was not
obtained.
At any rate, as Vincent reported, a project for the testing
of 8 additional liners was abandoned, and on March 12, 1936 the
93/ The justification for this conclusion is not clear,
inasmuch as an unplated 3-in. antiaircraft gun liner (No. 1183)
fired at a-different time showed an increase of 0.06Ц in. at the
origin after only 326 rounds, as contrasted with 6Ц0 rounds. A
careful comparison of the conditions of firing of these two guns
and of other unplated ones needs to be made; but unfortunately the
writer has not been able to find the records.
- 190 -
Ordnance Committee directed ’’that the development of chromium-
plating technic be closely followed by the Ordnance Department}
with a view to its possible consideration for gun-bore treatment
when the progress of the art appears to warrant such considera-
tion.” Up to the time of writing, no new trials of chrome-plated
cannon have been made, although early in 19Ц2 Watervliet Arsenal
furnished three oversize 37~ram tubes to the Van der Horst Corpora-
tion of America for experimental plating. Also, recent experiments
at the Battelle Memorial Institute have indicated considerable im-
provement in the technic of chrome plating [Russell, 19Ц2], tests
of which were made with their laboratory erosion gun (Sec. 88).
100.	Partially chrome-plated machine-gun barrels
A new idea in chrome-plating was developed during 19h1 at
Springfield Armory, namely, to plate only the breech end of the
bore where most erosion occurs. Use of a short anode for plating
only the first 7 in. of the bore of a caliber .30 machine gun
permits better control of the plating, and it also decreases the
cost. The plating is only O.OOO25 in. thick. One interesting
result of these experiments is that not only is the erosion
reduced, but also the muzzle velocity is increased, in one case
frbm 2610 to 27h7 ft/sec [Benson, 19h1]•
101.	British nickel-plated guns
As an economy measure, eroded gun tubes are now being
plated with nickel and then rerifled. This process, which
originally had been suggested by de Sveshnikoff and Haring [192h],
- 191 -
has been developed by the Research Department of Woolwich Arsenal
[A.C., 191i2a ]. The process, which involves the deposition of a
layer of nickel 0.1 in. or more thick at the breech end of the
bore, has about reached the stage at which it can be used on a
production basis for 3-7“ and li.3-in. antiaircraft guns [A.C. 19112b].
One of the plated 3-7“in. guns has been found to have an accuracy
life as long as that of a similar steel gun. After 7^0 rounds, nearly
one-third of which were bursts of 25 rounds each, the increase of
diameter at 1 in. from the origin of rifling was 0.1511 in. as com-
pared with 0.191 in. for the average of normal service guns. Some
flaking of the nickel plating had occurred. Ranging was normal
and accuracy was still satisfactory. The loss of muzzle velocity,
however, was greater than with a service gun [O.B.P., 19112a]. A
subsequent trial of two more barrels gave less favorable results.
9h/
One barrel showed poor accuracy after 100 E.F.C.—' and definitely
bad results after 1150 E.F.C. The. accuracy of the other was fair
up to about 1100 E.F.C. It was reported that "the complete trial
shows that satisfactory results may be achieved by this method of
repair, but that it is not yet reliable" [U.B.P. 191i2e].
911/ E.F.C. = equivalent full charge, which is the British
term corresponding to equiv-alent service round (see Sec. 12li).
- 192 -
CHAPTER XII. CONDITIONS' OF FIRING THAT INFLUENCE
THE RATE OF EROSION
ot/
102.	In previous sections—' the effect of various features of
the design of parts of the gun on the rate of erosion have been
considered. Of equal or even greater importance are the condi-
tions under which the gun is fired. Although the records of the
erosion of guns under varying conditions are not complete enough
96
to evaluate all the factors that conceivably might be suggested,—
they do indicate qualitatively the effect of some of them. The
present chapter gives a resume of the influence of a number of the
conditions of firing, illustrated by examples of data concerning
the rates of erosion of actual guns.
103.	Rate of fire -
It has long been known among artillerists that a rapid rate
of fire wears out a gun faster than a slow rate. This conclusion
has been confirmed frequently in proving-ground tests. Thus
Tolch [1936a, p. h] reported that the erosion produced in a
9$/ In Sec. 9 Part I, on Effect of design of rifling on ero-
sion, mention should have been made of the work of Jeansen L1936'j,
in which the results of calculations of the pressure on the sides
of the lands are given for different riflings in a 12-in./3O-cali-
ber gun. They show that although much of the pressure on the
lands at the origin of rifling can be eliminated by the use of a
rifling that starts with zero twist and then increases, a very
large pressure is then exerted on the lands during the forward two-
thirds of the travel of the projectile.
96/ Both Cranz [ 1926, vol. 2, p. 1 j and Schwinning [193b,
Chap. IV] have given extensive lists of such factors.
- 193 -
105-mm antiaircraft gun by 169 rounds of rapid fire was much greater
than that produced by 77O rounds of prior routine firing. The rate
of erosion at the origin of rifling during the first 770 rounds was
0.00018 in./rnd, whereas during the next 169 rounds it was
0.00025 in./rnd. The increase in erosion in the forward half of
the tube was even more marked. This gun was fired at its normal
muzzle velocity of about 2775 ft/sec in four bursts, three of which
were at the rate of 8 to 9 rnd/min and the fourth at half this rate.
A recent test, in which eight 13~lb barrels and three 9j-lb
barrels were fired under different conditions, resulted in the con-
clusion [Grant, 19Ц1 ] ’’that the erosion in the bore of a caliber .50
machine-gun barrel varies directly as; (a) length of the burst; .
(b) number of bursts; (c) cyclic rates; (d) lightness of the barrel;
and (e) velocity of the ammunition." This conclusion is in agree-
ment with those of earlier tests [Fleming', 1918]. One of these
tests illustrated the effect of continuous fire. Two caliber .30
Lewis aircraft automatic-rifle barrels were fired in bursts,of
approximately 500 rounds. At the end of the first 500 rounds ero-
sion was slight; but after 1500 rounds the rifling wore away rapidly.
The barrels became a bright cherry red, and the temperature of the
outside of the chamber as measured with an optical pyrometer was
978°C. The two barrels bulged just beyond the chamber after 2Ц25
and 2885 rounds, respectively, and a bullet passed through the wall
of one of them at the bulge. The steel used in these barrels had
the following composition: C, 0.20 percent; S. 0.91 percent; Mn,
О.ЦЦ percent; Or, 1.Ц7 percent; and V, 0.15 percent. Its tensile
Strength was 110/500 lb/in?, and its elastic limit was 75>OOO lb/in?
- 19b - '
ЮЦ. Temperature ’bf the barrel
The increase in rate of erosion with an increase in the rate
of fire is usually considered to be a result of the correspondingly
higher temperature of the surface of the barrel. A direct measure-
ment of this factor was made by Tolch [1935] who fired six caliber .30
Ml 919 Browning machine-gun barrels to destruction at different tem-
peratures, using two lots of single-base and two lots of double-
base powder. The temperature of the barrel was measured at first
by resistance thermometers and later by thermocouples welded 3«7
and 11.2 in. from the muzzle. After 100 to 200 warming rounds,
during which the temperature rose 1.3° to 1.9°C per round, 500 (or
1000) rounds were fired in bursts of 10 rounds at such frequency
as to maintain a predetermined temperature at 11.2 in. from the
muzzle. The accuracy life — corrected for warming and velocity
rounds — which was determined on the basis of the extreme spread
on targets at 1000 yards (see Chap. XIV, as given in Table XXVI.
Table XXVI. Accuracy life of machine-gun barrels fired at
different temperatures.
Temperature  (°c).	Accuracy Life (rounds)	
	Single-base Powder	Double-base Powder
200	19 050	21 000
300	12 180	10 830
hoo	9 060	6 650
Although with the same ammunition there was considerable variation
in the heat effects of the different barrels, the conclusion is
- 195 -
unmistakable that the life of the barrels fired at a- high tern-,
perature was shorter than that of the barrels fired at a lower
temperature..
105.	Muzzle velocity
The muzzle velocity of a gun is not an independent factor in
the rate of erosion, for it is dependent on the weight of the powder
charge, the weight of the projectile, the length of the gun and the
maximum pressure. Data are not available for an evaluation of the
separate influences of the length of the gun and the weight of the
projectile. For a given gun firing the same projectiles, of course,,
these factors are eliminated, and any increase in the rate of erosion
caused by an increase in muzzle velocity is due to the combined effect
of the increased powder charge and the resulting increased pressure.
It is convenient, therefore, to refer comparison of the rates of
erosion to this combined effect as expressed by the muzzle velocity,
although actually most of the increased erosion is probably due to
the increased charge, for the pressure itself, which is discussed
in Sec. 110, apparently has little effect on the rate of erosion.
Even for different guns, such as the three listed in Table XXVII,
the apparent inverse relation between the life of the gun and its
muzzle velocity probably is merely a reflection of the correspond-
ing variation of the weight of charge. The interpretation of this
comparison is complicated by the fact that the three guns were not
fired at the same pressures or with the same charge.
(a)	3~in. antiaircraft guns. — In a comparison of two nickel-
steel radially expanded 3-in. antiaircraft guns, one gun, No. 1(B-1),
- 196 -
Table XXVII. Comparison of life of guns and muzzle veloc-
ity.
. Gun	Length (calibers)	Tift, of Charge (lb)	Pressure (lb/in?)	Pro j.Wt. (lb)	Muzzle Vel, (ft/sec)	Est.Life* (rounds)
75-mm pack howitzer	15.93	1.0	26 000	15.0	1270	12 000
75-mm M1897A2	ЗЦ.5	2.0	36 000	ih. 7	1950	10 000
3-in. AA gun М2	55.0	6.0	111 000	12.8	3000	2 500
*Ord. Dept., 1936, Ii0-15, Table I, pp. 2-Ц.
was fired initially at 2600 ft/sec with an average "copper pressure”—
for 5 rounds of 26,800 lb/in? and the other gun, No. 2(B-2), was
fired initially at 3000 ft/sec with an average copper pressure for
5 rounds of 38,200 lb/in? The two guns were fired with the same
powder charges, whereupon the pressures and velocities decreased
gradually. .After 631 rounds, gun No. 2(B-2), which had been fired
with 6.5 lb of powder, had a velocity of only 276O ft/sec at a pres-
sure of 31,000 lb/in? The charge in this gun was increased pro-
gressively during the next 12 rounds, until it blew up at a pressure
of 113,200 lb/in? The corresponding decrease of velocity and pres-
sure in gun No. 1(B-1), which had been fired with 5-h5 lb of powder,
resulted in a velocity of 2Ц26 ft/sec at an average pressure of
23^700 lb/in? during rounds 723-727•
The increase in diameter at the origin of rifling of the gun
fired at higher velocity amounted to 0.181 in. on the lands and
97/ See Sec. 89(a).
- 197 -
0.126 in. in the grooves after 6Ц0 rounds. The corresponding en-
largements of the lower-powered gun after 6Ц0 rounds were O.O87 and
O.056 in. It required 1530 rounds to enlarge it to the same extent
as the higher-powered one had been enlarged after only 6Ц0 rounds.
At the muzzle after 6J4O rounds the higher-powered gun had increased
0.0$0 in. in diameter on the lands; the other not at all. Even
after 2200 rounds it had increased only 0.030 in. The rate of loss
of velocity was 0.32 ft/sec per round for the higherrpowered gun
and only 0.05 ft/sec per round for the other [Lane, 1933]»
(b)	h«7~in. guns. — The report of a recent endurance firing
of an experimental model of the U.S. Army’s new Ц.7-in. antiaircraft
gun not only illustrates the rapid erosion that occurs- at a muzzle
velocity of about 3Q00 ft/sec but also furnishes an opportunity to
compare this rate of erosion with that of another gun of the same
caliber fired at almost the same pressure with different charges
and hence different muzzle velocities. The muzzle velocity of the
50-lb projectile of this Ц. 7-iri. gun, T2, when the tube was newz
(rounds 16-20, inclusive) was 31 h2 ft/sec with a charge of 23.5 lb
of single-base powder, which gave an average maximum copper pressure
of 37,220 lb/in?; but with this same charge the muzzle velocity de-
creased, rapidly at first and then more gradually, to 2975 ft/sec
at the end of Ц00 rounds. The maximum pressure had dropped corre-
spondingly to 29,000 lb/inT	The erosion that had caused these
changes in pressure and muzzle velocity had been such as to increase
the diameter across the lands at the origin of rifling by 0.175 in.
at the end of Ц18 rounds. The erosion of the grooves had been about
- 198 -
half as great and, consequently, the distinction between the lands
and the grooves was lost at the origin of rifling. From an extra-
polation of the behavior of the gun for Ц63 rounds, the ’’economic
accuracy life'* [Sec. 125(f)], calculated on the basis of the proba-
bility of hitting an airplane under certain specified conditions,
was ihOO rounds. However, it was admitted in the report of this
calculation [Altschuler, 19hl] that, although no stripping of the
rotating band had been observed during the rounds fired, it is
probable "that the rotating bands of the projectile would be
stripped before the predicted accuracy life would be reached and,
therefore, that the stripping of the rotating band would determine
the actual life of the gun.’’
In contrast to the rapid erosion of this high-velocity h.7“in.
gun is the record of an earlier model, the U.7“in. gun M19O6. The
complete history of one of these guns is not available, but a record
[Ord. Dept., 1922c] has been found of the charges and copper pres-
sures during one period of the life of gun No. 808. Between rounds
22I4I4 and 2312, inclusive, lj.1 rounds were fired with a charge of
6.5 lb of powder at a mean-pressure of 30,050 Ib/inf The mean
velocity was 1703 ft/sec. The remaining 28 rounds were fired at
lower velocities, in the range 1529 to 1700 ft/sec. Thus, if this
sequence of firings may be considered representative, the pressures
in this gun were just about the same as in the h.7-in. gun T2, but
the powder charges were only about 30 percent as large. The muzzle
velocities were correspondingly some 1Ц00 ft/sec lower. The erosion
of tho lower-powered gun was so slight that a star-gaging after
- 199 -
3386 rounds showed an increase in diameter at the origin of rifling
of only 0.023 in. on the lands and 0.002 in. in-the grooves..
(c)	3-in./105-caliber gun. — A striking example of the ex-
tremely short life of a hypervelocity gun was furnished by the 
3-in./l0£-caliber gun, Mark’ XVI, No. 61-L, tested by the U.S. Navy
in 1922. This gun was fired Ц6 actual rounds, in nearly all of
which a charge of 17 lb of nitrocellulose powder was used. With
the 10-lb projectile that was used in most of the rounds, the average
muzzle velocity was Ц7^0 ft/sec at an average maximum pressure of about
Ц8,000 lb/in? The increase of diameter at the origin of rifling
amounted to 0.1Ц0 in. in this gun after Ц6 rounds, whereas in
82 3-in./5O-caliber guns fired at a muzzle velocity of 2700 ft/sec,
the average increase was only 0.028 in. after rounds 5 that is to
say, the erosion of the higher-velocity gun was five times as great
after only one-tenth as many rounds [Naval Ord., 1926].
(d)	The Paris gun. — The German long-range guns that were
used to bombard Paris during World War I were 21-cm guns — one
was rebored later to 21д cm — made by inserting a lining in a 38-cm
gun and having it extend beyond the muzzle of the original tube-.
The total length was 36 meters (17h calibers). The muzzle velocity
was 1^00 to 16OO meters/sec (Ц92О to 32Ц8 ft/sec) at a maximum
pressure of ЦЦ,000 lb/in? The probable life of one of these guns
was not more than 5>0 rounds [Miller, 1921].
106.	Type of propellant
The effect on erosion of difference in the kind of propellant
was early recognized, for it was the change from black powder to
- 200 -
smokeless powder that made the erosion of guns a serious problem.
After the experience of the Boer War, the British decreased the
proportion of nitroglycerin in cordite in order to reduce erosion
[Marshall, 1917* p. 30Ц]. According to Greaves, Abram and Rees
[1929, p. 122], ’’the change from cordite Mark I (calorific value,
1150 cal) to cordite K.D. (950 cal) trebled the life of big guns.
Similarly the use of nitrocellulose (810 cal) in place of cordite
98/
M.D. leads to increased life.”—
107.	Double-base versus single-base powder
(	The comparison between double-base and single-base powder is
illustrated by some recent data obtained in the endurance tests of
the 37-mm gun M1A2. For the first 500 rounds the increase in
diameter of the lands at the origin of rifling was the same
(0.00Ц in.) for a gun fired with du Pont single-base powder as for
another gun fired with Hercules double-base powder. Then the ero-
sion of the gun fired with double-base powder began to increase
rapidly, so that after 800 rounds, the lands had increased in
diameter a total of 0.01Ц in. while the lands of the other gun had
increased only 0,005 in. The increase in diameter of the grooves
was 0.009 in. after 800 rounds for the gun firing double-base powder
and only 0.001 in. for the other gun. The expected life of the gun
that had fired double-base powder was only 1800 rounds [Ord. Dept.,
19Ы> Report 13] compared with 3000 to 3500 rounds for the one
98/ See the quotation from O.B.P. [19h2d] in Sec. 108.
- 201
firing single-base powder in bursts of £0 rounds each with external
cooling between rounds [Ord. Dept., 19Ц1, Report 11].
In the test of machine-gun barrels already referred to (Sec. 10Ц),
half of the barrels were fired with single-base and half with double-
base powder. As is shown in Table XXVI, those fired with single-base
powder at 300° and ЦОО°С had the longer accuracy lives. The com-
parison at 200°C was complicated by the fact that one barrel was
fired with both single-base and double-base powder and had an actual
accuracy life of 27,770 rounds. The life of 21,000 rounds listed in
the table was an estimate of what would have been expected if the
barrel had been fired only with double-base powder. Furthermore, a
lower rate of fire was required with the double-base powder for the
maintenance of a given barrel temperature. Hence, as Tolch [193$}
p. 20] pointed out in his report on the test, ”if the barrels had
been tested at constant rates of fire, the differences in accuracy
life would have been considerably greater, other conditions being
equal, because of the greater heating effect of nitroglycerin-type
powder."
An important observation reported by Greaves, Abram and Rees
[1929, p. 123] was that cordite and tubular nitrocellulose (NOT)
powders produced the same sort of eroded surface. Two li.£-in.
howitzers of nickeL-steel and two 6-in. howitzers of nickel-chromium-
steel that had been worn out by firing one of each type with cordite
and one with NCT were examined. ’'There was no characteristic dif-
ference in the type of crack produced by either propellant. The
cracks in all instances were sharp at the bottom.! Their maximum
- 202 -
depth was about 0k05> in. in the tubes worn out with NOT and 0.03 in.
in those worn out with cordite, the apparent depth of the crack
being reduced by the ..more rapid erosion of the surface of the tubes
worn out with cordite. The character of the hardened skins and of
the surface cracking was the sane in each case, the difference be-
tween cordite and NOT being confined to the more rapid removal of
steel from the surface by cordite/*
108.	Picrite powders
The опЗу information at hand concerning the erosion produced
by picrite powders is the statement that "the erosion produced by
cordite N is about one-half that produced by American nitrocellulose
cannon powders. The erosion caused by cordite NQ is about equal
to that produced by American nitrocellulose powders.” [O.B.P.
19h1a.] No quantitative data were included. Another report
[O.B.P. 19h2c] suggests that in Q.F. ЦО-mm (Bofors) guns "the use
of NH propellant may bo expected approximately to quadruple the
life of the gun," compared with its life when firing cordite W.T.
In a later action the Ordnance Board recommended "that in all guns
one cordite full charge (ll.D., S.C., W or W.l-i.) should be reckoned
99/
as one E.F.C.,— nitrocellulose full charges (NH or FNH) and
cordite NQ as half E.F.C. and cordite N as quarter E.F.C." [O.B.P.
19h2d].
99/ See footnote 9h.
- 203 -
10?. Erosion vent plug tests
The relation between the adiabatic explosion temperature
(Sec. 36) of the propellant and the rate of erosion was investigated
by de Bruin and de Pauw [1931J»	In two series of experiments at
pressures of 1^,500 and 20,000 lb/in?, erosion vent plugs of
"Silberstahl’* (0, 1.28 percent; Mn, 0.31 percent; Si, 0.20 percent;
P, traces; S, 0.029 percent)^ having axial holes 1 mm in diameter
and 25 mm long, showed losses of weight that were linear functions
of the temperatures of combustion as computed from the composition
of the smokeless powder. These computations were based on the
authors' previous measurements [de Bruin and de Pauw, 1928] of such
temperatures as a function of composition. The temperatures ranged
from 2б750 to 35?5°C. It was also found that two powders of very
different composition but having the same combustion temperatures
produced the same amount of erosion.
110.	Pressure
The effect of pressure on erosion is difficult to evaluate,
because in guns of the same design any marked increase of pressure
must be obtained by an increase of charge. Hence any variation of
the rate of erosion may be ascribed to either^ cause. Vieille [1901]
suggested that the pressure affects erosion indirectly by deter-
mining the amount of gas that flows through a crack. This sugges-
tion, which is bound up with Vieille*s theory of the mechanism of
erosion (see Sec. 11Ц), has been neither proved nor disproved.
(a)	6-pounder guns. — One occasion on which two guns of the
same caliber were fired at different pressures with the same charge
- 20Ц -
of powder was when two. new 6-pdr. guns — Mark III, No. 18,
American Ordnance Co., and Model 1900, No. 3h* Driggs Seabury
R. F. — were fired a total of 995 rounds each., in two series,
at a muzzle velocity of approximately 21j00 ft/sec. During the
first series of 600 rounds, gun No. 3h was fired with slow-burning
powder and gun No. 18 with quick-burning, and during the second
series of 395 rounds, the powders were interchanged. The slow-
burning powder was U.S. Navy 6-pdr. S. P. 592, web 0.03h in., and
the quick-burning powder was U.S. Navy 3-pdr. S. P. 53h, web
0.023 in. The mean pressures were about 32,500 lb/in? with the
former and 37*000 to 38*000 lb/inf with the latter. After 600
rounds the erosion in the rear portion of the rifled bore of the
gun firing the quick powder was very slightly greater than that
of the other gun. The difference was described as 11 inconsiderable.11
After 995 rounds the wear on both guns, which was not near the limit
of endurance, had been approximately equalized by the interchange of
powder [Ord. Dept., 1907]» From this experiment we may judge that
the difference of 15 percent in the maximum pressure had practically
no effect on the rate of erosion of these guns.
(b)	Ц.7-in. guns. — The comparison of the erosions of a
!
h.7_in. gun and а Ц. 7-in. howitzer, already cited in Sec. 105(b),
shows clearly how little influence the maximum pressure per se
has on the rate of erosion. It seems that only with reference to
a particular gun, firing a certain kind of powder, is the maximum
pressure related to the rate of erosion, and then only as an index
of the amount of charge.
- 205 -'
(c)	Erosion vent plug tests of propellants. — The corre-
sponding effect in the case of erosion vent plugs is shown by the
results of two series of experiments at pressures of 1050 and 1350
atmos and at different temperatures ranging from 2675° to 3575°C,
made by de Bruin and de Pauw [1931] The extent of the erosion
of the plug was a linear function of the temperature for each
pressure, that is, the extent of the erosion was increased by the
same absolute amount at all temperatures; and hence at the low
temperatures, where the erosion was slight, the proportional effect
of the increase in pressure was-much greater than at the higher
temperatures.
111.	Lubrication of the bore
Lubrication of the bore of a rifle or handgun firing plain
lead-alloy bullets is essential to prevent the barrel from becoming
’’leaded,'1 as described by Sharpe [ 1 9Ц2, p. 81]. The lubricant
ordinarily is applied to the bore by putting it in the cannelures
cut in the body of the bullet. It consists of a mixture of several
of the following constituents, the proportions of which vary accord-
ing to the whim of the handloader: carnauba wax, ”Japan” wax, bees-
wax, tallow, ozocerite, mineral oil, castor oil, graphite, and
J
sodium aluminum stearate (dictaphone-records shavings).
112.	Lubrication of bullet by base wad
Another method of lubricating a rifle bore that was in vogue
in the days of black powder was to place a wax wad on the base of
the bullet before inserting it into the cartridge case. The wad
- 206 -
was cut from a thin sheet of wax of the desired composition. This
practice, which is still used by some riflemen when firing lead
bullets, has been extended recently to the firing of high-velocity
metal-case bullets. Sharpe [ 19Ц2, p. 8Ц] claims that the wax wads
he has used with both the .220 Swift and the .257 Roberts cart-
ridges ’’not only improve accuracy, but practically eliminate ero-
sion when light bullets are driven at velocities above Ц000 ft/sec.11
He goes on to quote [Sharpe, 19U2, p. 85] J. B. Sweany, one of the
originators of the .220 Swift cartridge, as having stated that
"all Swift loads require grease wads for best results, both in
reducing erosion and producing maximum accuracy. ц A wax wad
especially recommended by Sharpe for this use contains colloidal
graphite in the form of Oildag, which he claims [Sharpe, 19h2, p. 85]
penetrates "the pores of the barrel metal under the pressures
developed during firing, thus sealing these pores and greatly re-
ducing wear on the barrel." Lubrication of small arms bullets for
military use has never been adopted by the Ordnance Department of
the U.S. Army on the grounds that it would be a useless practice.
113* Lubrication of artillery projectiles
Artillery projectiles have been lubricated at times. Thus
during World War I the Italian army used an asbestos band impreg-
nated with wax and tallow. The French greased the outside of
shells; and instructions were issued to the A.E.F. to grease the
155-mm howitzer projectiles, apparently in acceptance of tho
current French practice. The Ordnance Committee in 1922, however,
approved a report by a subcommittee recommending that this practice
- 20'7 -
be not followed on the grounds that the grease may cause the intro-
duction of dirt into the bore, that the use of grease is an unneces-
sary expense and inconvenience, and that tests at Aberdeen Proving
Ground with greased projectiles in 75>_™. guns had shown no decrease
in erosion. Details concerning these tests have not been located.
Limited trials by the U.S. Navy of experimental projectiles having
cannelures filled with graphite and grease did not indicate any
improvement with respect to either erosion or coppering.122/
Similarly, Greaves, Abram and Rees [1929* p. 123] reported
that ”a comparative examination was made of two 60-pdr. guns, each
of which had fired about h5>00 equivalent full charges of cordite
M.D. One had been lubricated with wool grease throughout the last
two-thirds of its life and the other had been worn out dry. The
main differences observed were a slightly greater maximum depth of
scoring in the nonlubricated gun, and rather more coppering in the
lubricated gun. The character of the surface cracking was almost
identical at similar positions throughout the tubes."
In spite of these negative results, the use of a bore lubri-
cant as a cure for erosion is suggested probably more often than
any other remedy. The a .priori reasoning is sound, being based
on the proven value of a lubricant such as graphite in reducing
wear on metal dies. The lack of similar success with the use of
a lubricant in the bore of gun may be due either to the operation
of other more powerful causes of erosion or else to improper
100/ Lt. B. D. Mills, personal communication
- 208 -
application of the lubricant. In this latter respect the ”J”
band having cannelures at the front end, which is discussed in
Sec. 122, would seem to represent about the best means of apply-
ing a lubricant to the bore surface at the point of contact be-
tween the rifling and the rotating band.
- 209 -
CHAPTER XIII. EFFECT ON EROSION OF
LEaKAGE OF GAS PAST THE PROJECTILE
11Ц. Theory of gas leakage
Although doubts have often been expressed as to how well,
the rotating band performs its function of obturating the bore,
there seems to have been no systematic experimentation to determine
whether it does or does not. Consequently, most of the writings
concerning the influence of gas leakage on erosion have been
speculative. Lanfroy [1885] and Bourgoin [1913] supposed that this
leakage takes place through a crescent-shaped opening between the
projectile and the bore, caused by dilation of the bore by the
pressure of the powder gases. Vieille [1901], who was the leading
exponent of the theory of gas leakage, supposed that it takes
place principally through the small openings that result from
failure of the rotating band to mold itself into the fine cracks on
the surface of the bore (Sec. 70). He argued that the particular
openings through which leakage occurs change from moment to moment
as the rotating band moves forward; and that therefore it is only
at the breech end of the bore that the rotating band is moving
slowly enough for a given set of cracks to remain in action long
enough to cause much erosion.
Charbonnier [1922, pp. .100Ц-10С5], on the other hand, who
opposed Vieille*s theory, stated that projectiles fired without
rotating bands gave the same velocity and pressure as was obtained
with the' same kind of projectile fired with bands. He claimed that
- 210 -
the same was true of a tubular projectile. He suggested that these
phenomena indicated that as the projectile moves forward it carries
with it an annulus of gas that acts as an obturator.
The best exposition of the objections to the theory of gas
leakage was given by Alger [1910] in a paper written in reply to
the one by Yarnell [1910] mentioned in the next section. He
pointed out five objections to the theory, which may be summarized
as follows: (i) the rate of wear of the smooth bore just at the
rear of the rotating band is the same as that of the bottoms of
the grooves at the origin of rifling; (ii) the lands erode twice
as rapidly as the grooves; (iii) the opportunity for gas leakage
should be greater halfway down the bore, because of wearing of
the copper rotating band, than at the beginning of travel; (iv)
the erosive effect of the gas that escapes past the projectile
depends solely on the temperature and pressure of that gas, which
conditions are the same in low-powered and high-powered guns
firing the same kind of powder at the same maximum pressure,
although these guns erode at different rates; and (v) the rotating
bands of fired projectiles show no erosion.
115.	Vent plug experiments
The erosion vent plug experiments performed by Vieille
[Sec. 9h(a)] were offered as evidence of the erosive effects of
hot powder gases rushing through a small opening with a high veloc-
ity. Neither he nor Yarnell [1910], who espoused Vieille's theory
and who reported additional erosion vent plug experiments, performed
- 211
any other experiments that more closely simulated the conditions
in a gun.
A special vent plug experiment reported by Yarnell consisted
of placing a can containing water on 'the inside of the chamber in
such a manner that the water was forced out through two pinholes
into the top of the chamber near the vent. He found that in this
way the erosion of the vent plug was reduced to a third of its
former value. He suggested that in a gun, erosion similarly might
be reduced by having a circular receptacle containing water — or
other liquid — at the rear of the projectile so that it would
burst upon the shock of firing and would permit the water to seal
the bore before and shortly after the projectile begins to move.
Yarnell suggested that "as the necessity for such a seal exists
for an exceedingly small fraction of a second, not much liquid
would be required, and its high latent heat would effectively cool
such small percentage of the total volume of gas as would escape
past the projectile." There is no record that Yarnell’s sugges-
tion has ever been tried,
116.	Photography of gas leakagel^/
High-speed photographs of a large projectile coming out of
the muzzle of a gun were cited by Dr. L. ,T. E. Thompson—as sup-
porting evidence that leakage of gas is not an important factor in
101/ Photographs of the gas' that leaks past,a rifle bullet
when fired into a vacuum are being taken at the Geophysical Labora-
tory.
102/ Personal communication, September 19U1.
- 212 -
erosion. These photographs show that only a ’’small” amount of
gas escapes ahead of the projectile in comparison with what comes
out behind it; but inasmuch as there is no way to estimate the
actual quantity of this gas, the evidence is not convincing.
117.	Escape of gas through holes drilled in the shot
Greaves, Abram and Rees [1929, p. 119] described an experi-
ment that caused them to conclude that leakage of gas past the
projectile was a negligible factor in erosion. Inasmuch as it
represents about the most thorough investigation of the subject
that has been made, their description is quoted in full:
It has been suggested by Vieille that not only is
scoring due to escape of gas past the driving band, but
that normal erosion is also due to such escape through
the minute channels existing in the cracked surface layer.
It is a matter of importance to determine the minimum
size of orifice through which gas can pass without under-
going sufficient cooling to render it inactive as an
erosive agent. Two 18-pdr. proof shot were drilled
longitudinally, one with a central axial hole 0.$ in.
in diameter, and the other with four holes each 0.25 in.
in diameter, spaced symmetrically relative to the axis
of the shot and to each other. The two shot were then
fired under the normal conditions adopted for solid
18-pdr. proof shot, with, the following results:
18-pdr. Proof Shot	Weight of Projectile	Muzzle Velocity (ft/sec)	Maximum Pressure (tons/in?)
Solid	18 lb,8 oz	1677	13.65
Drilled with hole 0.5 in. in diam.	18 lb,1| oz	1602	12.35
Drilled with h holes 0.25 in. in diam.	18 lb,l£ oz	1607	12.65
There was thus a decrease in recorded pressures and
muzzle velocities relative to those obtained for solid
shot.
- 213 -
The fired shot was sectioned. Microscopical exam-
ination of the metal in the neighborhood of the holes
showed the presence of a hardened-slowly-etching sur-
face layer. The structure at a position near the nose
of the shot drilled With four holes is shown in
Fig. 16 (Plate IV). The depth of this hardened skin
appeared to be constant throughout the length of the
shot, andwas 0.003^ in. for each shot. Brinell
hardness measurements made with a 1-mm- ball and 30-kg
load on the bore surface of the drilled holes gave
ЗЦ1 in comparison to 220, the normal hardness of the
material of the proof shot.
It was thought desirable to employ a smaller ori-
fice, but a hole much less than 0.25 in. in diameter
could not be bored, through the full length of a proof
shot. Two 18-pdr. proof shot were therefore drilled
with axial holes 0.5 in. in diameter. The forward
end of these holes was then fitted with a plug of
annealed 0.8-percent carbon steel. This steel (the
same type as was used for the cylinders subjected to
chamber conditions during firing) was chosen because
it is sensitive to the formation of a hardened skin
and has poor resistance to erosion. The plug in one
shot was drilled with an axial hole 2 mm in diameter,
while the other was drilled longitudinally with
Ц holes each 2 mm in diameters
18-pdr. Proof Shot	• Weight of Projectile	Muzzle Velocity (ft/sec)	Maximum- Pressure (tons/in§)
Solid shot	18. lb,8 oz	I672	13. Ц0
Shot fitted with plug with 1 hole, 2 mm in diam.	18 lb,L|. oz	1668	13.35
Shot fitted with plug with Ц holes, 2 mm in diam.	18 lb,3loz	1659	... 13Л5
There was thus no diminution in maximum pressure,
and only a slight loss in muzzle velocity.
The plugs were weighed before and after the proof
shot had been fired; the loss of weight on firing.was
0.180 gm for the plug containing one hole, and 0.233 gm
for that with four holes. As the plugs suffered some
slight abrasion in the sand bay, these figtires may bo
' rather too high, but evidence of the passage of pro-
pellent gases through the plugs was afforded by the fact
- 21Ц. -
that along all the holes there was a slowly-etching hardened layer,
which appeared to be of a constant depth of 0.0022 in.
throughout the length of the plugs.
In order to ascertain whether there had been any
escape of gas past the driving band, the surface of the
shot was examined by etching, but there was no trace of
a hardened skin due to gas-washing. ^Thus, these ex-
periments, while they show that gas passes through a
2-mm orifice in the proof shot at some tine during its
passage down the bore, fail to indicate (in thg case of
a new 18-pdr. gun, at least) that there is any escape of
propellent gases past the driving band during the
initial stages of motion.
118.	Gas leakage in a worn gun
As a continuation of the experiment just described, Greaves,
Abram and Rees sought for evidence of gas leakage in a worn gun.
They reported as follows:
Some Ц-in. proof shot fired in a worn Ц-in. Mark V gun
(mean wear at 1 in. from commencement of rifling, 0.039 in.)
were examined. One of these showed a hardened skin (maxi-
mum thickness, 0.0010 in.) produced by gas-washing for-
ward of the driving band. The driving band itself showed
some signs of gas-washing. Four other shot fired in the
same gun showed no hardened skin on the side of the shot.
It seems, therefore, that the formation of a hardened
skin, indicating gas-washing, on the projectile forward
of the driving band, is not a necessary consequence of
the worn condition of the bore (except possibly when
scoring is already very pronounced), but is fortuitous
and due to occasional faulty ramming or bad centering
of the projectile in the gun. In a worn quick-firing
gun firing fixed ammunition, however, the same effi-
ciency of obturation could not be obtained.
119.	Undersize rotating bands
In a recent experiment with rotating bands, projectiles having
bands that differed in diameter were fired with single-base powder
from two new 37“ьтп guns. After 800 rounds, each gun had eroded
only very slightly; there was an increase in diameter of 0.005> in.
- 215 -
across the lands at the origin. The advance of the forcing cone
was also essentially the same '— 0.035 in. for the large bands
and 0.0Ц5 in. for the small ones. This result, which by itself
would have been inconclusive, assumes new significance upon com-
parison with the result obtained when some of the same projec-
tiles having rotating bands of normal diameter were fired from
another new gun with double-base instead of single-base powder.
At the end of 800 rounds this gun had eroded O.Olh in» at the
origin and the forcing cone had advanced 0.20 in. Hence it may
be concluded that the use of the small-diameter rotating bands,
the diameters of which were slightly less than that of the grooves,
had far less effect on the erosion of one of these 37-mm guns than
the use of double-base powder compared with single-base [Ord. Dept.,
19Ы].
120.	Obturation by bullets
The obturating action of a small arms bullet is different
from that of a banded projectile, for the whole jacket of the
bullet acts as the rotating band. In the case of a lead-core
bullet, obturation is aided by the ’’upsetting" of the bullet, that
is, the increase of diameter caused by the sudden application of
the accelerating force of the powder gases. The increased erosion
that armor-piercing bullets are supposed to cause may be due to
the lack of upsetting and hence to poorer obturation.
The use of a bullet that is a force-fit in the throat of a
rifle just behind the forcing cone is reputed to eliminate erosion.
- 216 -
Mr. Niedner, of the Niedner Rifle Manufacturing Company, once
told Mr. J. C. Gray, Ordnance Engineer of the Ordnance Depart-
ment, that Mr. Mann, the amateur rifle expert, fired such bullets
about 191$, and found nb erosion of a caliber .2$ rifle after
1f>,000 rounds.!^/ It is not known whether a control test was
made with normal bullets, and so it is questionable whether the
erosion of a rifle of this small caliber could have been detected
after that number of rounds.
121.	Gas checks
Some experimental firings have been made with projectiles
having special obturators or gas checks attached to them. Thus
different modifications of a device invented by J. H. Brown were
tested at Aberdeen Proving Ground from 1907 to 1911 л without any
marked decrease in erosion having been noted. Another obturator
that was tested at Aberdeen was reported [Feltman, 1929] to have
increased rather than decreased the erosion. The exact design of
the device was not given in the report of the firing, but it seems
to have consisted of some sort of cardboard wad at the base of a
3-in. projectile. The increased erosion was ascribed to the
11 sandpapering effect’* of the bits of cardboard that were blown
down the bore.
122.	Rotating band with forward gas seal
If obturation by the rotating band is important, 'then a very
sensible suggestion concerning the position of the gas seal is
103/ J. G. Gray, personal communication, 19Ц1.
- 217 -
that made Recently by Commander F. G. L. Johnson, (British) Royal
Navy (retired). In the ''J” band that he has patented, Johnson
[19Ц2] claims that the lubricated seal formed by the front end of
the rotating band is unaffected by the dilation of the bore of the
gun by the gas pressure. This seal is obtained by having several
narrow cannelures which are cut in the front end of the\band filled
with a heavy grease ("Tropilene E," melting point 32O°F). The
cannelures are close together, so that ’'when the shell is loaded,
the front tiro or three ribs [of copper that separate the cannelures]
are deformed to the rear due to contact with the band seating, and
grease is extruded, thus creating a gas-tight joint. As the lands
cut through the ribs and grooves during engraving, they force the
grease in a circumferential direction, which action has the bene-
ficial effect of forcing the portions of ribs located in the rifling
grooves to the front, thus keeping them in close contact with the
bottom of the groove to maintain the seal." Commander Johnson
stated that firing tests, of which he gave no details, have sub-
к
stantiated his claims, and that the British Ordnance authorities
are giving serious consideration to his proposal.
Somewhat the same end is achieved by certain features of the
so-called ”R. D. System of Rifling” (Sec. 126), which has been
developed recently by Colonel G. 0. C. Probert and others in the
Research Department of Woolwich Arsenal. A projectile having two
bands is used and the forcing cone is moved forward slightly. The
rear band, which fits tightly in the smooth cylindrical throat of
the gun, is supposed to seal the bore while the front band is being
- 218 -
engraved. Then, after the rear band has been engraved, the
front band can continue to make the gas seal even if the bore
is dilated at the rear band. The R. D. System of Rifling has
been tried recently with considerable success in the reduction
of erosion. Thus, in two quick-firing 3. 7“in« antiaircraft guns
with muzzle velocities of about 3h00 ft/sec the maximum erosion
in the one of conventional design after 80 rounds was O.O73 in.,
whereas in the modified gun it was only 0.0Ц8 in. after 80 rounds.
The other feature of this design, as will be described in Sec. 123(d),
is that the effect of erosion on ballistic performance is mini-
mized [Naval Intell., 19Ц2].
- 219 -
CHAPTER XIV. LIFE OF GUNS
123.	The life of a gun is not a fixed mathematical quantity but
is a statistical average, analogous to a life expectancy for a human
being. Because of variations in the manner of their use, several
guns of the same kind will have widely different lives. Some of
these variations, such as rate of fire, amount of charge and kind of
powder, have already been discussed in Chap. XII, but it is likely
that there are other less well-defined conditions that also affect
the life of guns in service.
12Ц. Formula for equivalent service rounds
One of the most important variations of firing conditions is
the amount of charge, because scarcely any erosion occurs when a gun
is fired with a charge considerably below the "service charge” for
which it was designed. Sometimes at the beginning of a firing a
reduced charge is used for the first round or two, just for the
purpose of warming the gun. In the U.S. Navy, for the purpose of
tabulation, such warming rounds or any other round fired at other
than the standard charge are converted into equivalent service rounds —
E.S.R. — by means of the formula,
E.S.R. = (W/We)^	(XlV-la)
Ь
where W is the weight of the charge actually used and W_ is the
weight of the service charge.
- 220 -
Another formula for the same purpose was developed by
Feltmanl2k/ empirically on the basis of the values of E.S.R. for
various charges of nitrocellulose powders as given in various
British firing tables and then checked against the values of E.S.R.
used in the U.S. Navy. This formula, which is intended to take
into account the effect of the reduced pressure that accompanies
the decrease in weight of charge, is
p
E.S.R. = (V/V_),	(XIV-1b)
where V is the muzzle velocity at which the gun was fired, V_ is
the standard muzzle velocity, and g is an empirical constant taken
equal to 7 when V/V„ >0.6 and equal to 5.5 when V/V_ < 0.6. Both
these formulas indicate a large increase in the life of a gun when
it is fired with reduced charges. For example, during the accept-
ance test of some 37-mm powder a charge of Ц.00 oz gave a maximum
pressure of 21,500 lb/in? and a muzzle velocity of 2339 ft/sec,
whereas a service round required Ц.70 oz of the same powder to give
the standard velocity of 2596 ft/sec (nominally 2600 ft/sec) with
a maximum pressure of 28,600 lb/in? The round fired at reduced
charge, therefore, was 0.Ц E.S.R. according to Eq. (XIV-1a) and
0.5 E.S.R. according to Eq. (XIV-1b). Correspondingly, a round
fired in the same gun with a charge of Ц.oz of the same powder,
which gave a muzzle velocity of 268Ц ft/sec at a maximum pressure
of 31jU50 lb/in?, was equivalent to 1.35 E.S.R. according to
10h/ S. Feltman, Ballistics Section, Ordnance Department,
personal-communication.
- 221
Eq. (XIV-1a) and to 1.26 E.S.R. according to Eq. (XIV-1b). Thus
Eq. (XIV-1b) indicates less of a variation from unity than does
Eq. (XIV-1a), for charges either more or less than standard.
125.	Criteria for end of life
Another complication in considering the life of a gun is that
there is no unambiguous point in its history that is considered the
end of its life. As erosion proceeds during use, the muzzle velocity
gradually decreases, because of the advance of the forcing cone [see
Sec. 125(d)], and also the dispersion of the. shots at a given target
increases. However, the decision as to just how much of a decrease
in muzzle velocity or how large a dispersion can be tolerated is purely
arbitrary. Moreover, this decision depends to a certain extent on
the tactical purpose of the gun.
(a)	Loss of muzzle velocity. — Some writers have suggested
that the time when a gun has lost 10 percent of its initial muzzle
velocity should be considered the end of its life. This criterion,
according to Lintes [1935] corresponds to a loss of 50 percent in
precision and an appreciable diminution of range. A ‘somewhat more
severe criterion--—/ is actually used now by the Small Arms Division
of the Ordnance Department with respect to the- caliber .50 machine
gun. When the muzzle velocity of this gun — which is 2800 ft/sec
when the gun is new — has decreased 200 ft/sec, the gun is con-
sidered to be at the end of its accuracy life. This usually occurs
ЮЦа/ Capt. С. E. Balleisen, personal communication,
August 19h2.
- 222 -
after about 8000 rounds. Further firing would be possible, but
the sights would have to be adjusted for the decreased velocity,
which causes the gun to hit below the target.
(b)	Dispersion in range. — In the U.S. Navy the mean dis-
persion of five successive shots fired at a target at a given range
is usually used as the basis of the criterionl2£/ for determining
the end of life of a gun. Yilhen this mean dispersion exceeds
0.5 percent of the range for a major-caliber gun — 8 in. and
larger — or 1 percent for a smaller gun, the end of accuracy life
is usually' considered to have been reached. There is no regula-
tion, however, on this question, and not all guns are rated in this
way.
(c)	Enlargement of the bore. — The loss of muzzle velocity,
and hence the life of a gun, has frequently been correlated with
the extent of erosion as expressed by the increase in diameter of
the lands at the "origin of rifling" (really at the front end of
the forcing cone) or at a point 1 in. in front of the true origin
of rifling. The decrease in muzzle velocity for most guns is a
linear function of the increase in diameter, the constant of propor-
tionality being a function of the caliber and muzzle energy of the
gun. Manning [1 919], for instance, found that in the expression,
AV = 100 Ky,
(XTV-2)
where AV is the loss of muzzle velocity in feet per second and £ is
105/ Lt. B. D. Hills, personal communication, August 19h2.
- 223 -
the increase in diameter of the lands in inches at a point 1 in. in
front of the origin, the empirical constant К varied from 2.3 to
12.1 for eight guns of different calibers, being larger for small
calibers.
Practical use is made of this relation at proving grounds in
connection with so-called "work guns," which are used for acceptance
tests of powder. The end result desired is the relation between
muzzle velocity and weight of charge when the powder is fired in a
new gun. A given weight of charge fired in an eroded work gun gives
a somewhat lower muzzle velocity than would have been obtained in a
new gun. The muzzle velocity characteristic of a new gun is obtained
by an extrapolation based on the measured erosion of the work gun and
the relation between muzzle velocity and the increase in diameter at
the origin.
The end of life of some U.S. Navy guns is considered to be
reached when the enlargement at 1 in. in front of the origin of
rifling has reached a certain magnitude. For 1 Ц-in./50-caliber guns
the permissible maximum enlargement is 0. Ц in. For such high-
powered guns the application of this criterion is complicated by the
fact that they are subject to considerable muzzle erosion, which also
affects the accuracy .life; and therefore, as already mentioned in
Sec. 98, a duplex criterion involving erosion at both ends of the
bore is used.
(d)	Advance of the forcing cone. — Another direct measure
of erosion that has been correlated with gun performance is the.advance
of the forcing cone (Sec. 10) as measured with a plug gage. This
- 22Ц -
measurement is much simpler than that of the increase in diameter
across the lands and therefore is more readily performed in the
field. The ЦО-mm Bofors gun now being used by the U.S. Services,
for instance, is supplied with such a gage.
The advance of the forcing cone is reflected in the perform-
ance of the gun. In an eroded gun using separate-loading ammunition
the projectile can be seated correspondingly farther forward in the
bore. Thus for some worn 155-mm guns, G.P.F., when the forcing cone
had advanced h.O in., the seating had advanced about 2.5 in., and
when the forcing cone had advanced 8.0 in., the seating had advanced
6.75 in. [Weyher, 1939)• The decrease in the density of loading
that results from the advance of the seating of a separately loaded
projectile causes a decrease in the pressure and velocity. The re-
duced travel of the projectile also decreases the velocity slightly.
In a case gun the projectile remains in the cartridge case until the
powder is ignited; but as soon as a little pressure is developed,
the projectile is able to move forward nearly the whole distance
that the forcing cone is advanced. This free run-up has about the
same effect on the maximum pressure and the muazle velocity as the
advance of seating in a bag gun. In addition, it tends to cause
stripping of the rotating band [Sec. 125(e)].
The relation between loss of muzzle velocity and advance of
the forcing cone is nonlinear for most guns; but in spite of this,
the advance of the forcing cone can be used as a criterion of the
end of life. This was done in World War I by the French and sub-
sequently by the A.E.F. when using French guns. For the 155-nm gun,
- 225 -
for instance, the criterion was an advance of the forcing cone of
150 mm. It had been found that beyond this point, which was reached
after 3500 + 500 rounds, a maximum of Ц00 more rounds could be fired
[Ord. Dept., 1920]. This criterion was confirmed by a later study
of the characteristics of a number of 155-mm guns at different stages
of erosion (see Table XVI, Sec. 61).
(e)	Stripping of the rotating band. — Any arbitrary criterion
of the life of a gun, such as the enlargement at the origin or the
advance of the forcing cone, has the disadvantage that frequently
during actual service a gun can still be fired after the measured
erosion indicates that it has reached the end of life. The gun will
not perform as satisfactorily as a less worn one, but it will be
much better than no gun at all. This situation occurred during
World War I, when the French twice found it expedient to relax the
regulations concerning the replacement of 75-nim guns in the field.
Such continued use of an eroded gun cannot go on indefinitely,
however, when the gun fires fixed ammunition. Eventually the fbrcing
cone is advanced to such an extent that the projectile attains so
high a velocity by the time its rotating band hits the forcing cone
that the upper surface of the band is sheared off by the rifling and
the projectile is not rotated. When this occurs the projectile
tumbles in flight. This stage of erosion of the- gun truly represents
the end of its life, for accurate firing is no longer possible. It
has frequently been used as the criterion of the end of accuracy
life in erosion tests of small arms, the occurrence of keyholes in
a close target giving the indication of when it happens (see Sec. 82).
- 226 -
(f)	Economic life. — An artificial criterion of the end of
life of a gun has been considered in at least two recent erosion
studies of army guns, namely, those of the 155-mm gun (Sec. 61) and
of the h.7-in. gun [Sec. 105(b)]. This criterion, which is called
the economic life, is defined as the maximum number of rounds that
can be fired at a minimum cost per round, taking into account the
replacement cost of the gun and the increasing cost of ammunition
per hit as the accuracy decreases because of erosion. This
criterion is without real significance, because it presupposes an
abundant supply of guns. In effect, the replacement cost of a gun
.is infinite during an engagement when the replacement gun.is not
available.
126.	The R.D. system of rifling and banding^-^^
The basic feature of the special design of rifling and of pro-
jectile banding which is known as the '*Probert!* or !,R.D. System’*
is an attempt to prolong the accuracy life of a gun by minimizing
the effects of erosion as well as by reducing the erosion itself.
To this end the.original contour of the bore is made to approximate
that of a somewhat eroded barrel and then the projectile is designed
to function well in such a bore, by reducing the extent to which its
resistance to movement at the beginning of travel changes as erosion
proceeds.
106/ See Sec. 136 for the decrease of muzzle erosion observed
with the R.D. system.
- 227 -
This is accomplished by a combination of (i) making the initial
resistance to Movement as small as possible in a new gun and (ii)
making the proportional decrease of resistance for a given increase
of wear as small as possible. The former end is achieved by making
the slope of the forcing cone as small as is consistent with .the
need for sealing the gas as quickly as possible and by reducing to
the minimum the quantity of copper that has to be displaced when the
shot starts to move. The latter end is achieved by making the
diameter of the.upstanding copper in the rotating band exceed that
of the bore by the greatest practicable amount in order to dwarf
the effect of the wear in the bore on the rate at which this copper
is displaced after shot travel^ An attempt is made to reduce the
erosion itself both by improving the gas seal (Sec. 122) and by
placing the origin of rifling farther from the mouth of the cartridge
case.
The few trials that have been made of this system have shown
very favorable results. Thus, in the two quick-firing 3.7“in. guns
mentioned in Sec. 122, there was a marked difference in the effect
of erosion on muzzle velocity. Whereas in the conventional gun
the velocity had decreased ft/sec after 81 rounds, in the modified
gun it actually increased 63 ft/sec after 80 rounds, even though the
bore of the latter gun had been increased two-thirds as much as that
of the former
- 228 -
127.	Navy-formula for the life of guns-—
A general formula for erosion in U.S. Navy guns was proposed
by Captain G. L. Schuyler [Bur. Ord., 1928]. As a preliminary
step to developing tabulated numerical functions of the several
variables on which the life of a gun depends, he expressed the
average bore enlargement per round, E, during the first 100 rounds
by the equation
log E =log А- 1.5Ц log 1 -16.Ц log d+12.0 log V+6.0 log M, (XIV-3)
where E is measured in inches at a point 1 in. in front of the origin
of rifling, 1 is the length of the gun in calibers, d is the diameter
of the bore in inches, V is the muzzle velocity in feet per second,
M is the projectile weight in pounds, and A is an empirical con-
stant. This constant and the other four in the equation were evalu-
ated from data for 12 guns that ranged in caliber from 3 to 16 in.,
in length from 23 to 103 calibers, in muzzle velocity from 2200 to
Ц800 ft/sec, and in projectile weight from 10 to 3100 lb.
The observed bore enlargement of naval guns at the end of
life was combined [Bur. Ord., 1935] with Eq. (XIV-3) to yield the
following formula for the accuracy life of a gun in E.S.R.:
N = 0.1080 d2/3 E"1	(XIV-U)
This formula was subsequently modified [Bur. Ord., 1939b], in order
to take into account recently acquired experimental evidence of the
10?/ See Sec. 130 for a comparison of this formula with others.
- 229 -
lack of effect of the weight of the projectile on erosion when the
muzzle velocity is constant and to permit the calculations to be -
performed by means of equations, instead of tabulations. The modi-
fied formula is
log N = 6.35 + 0.03 1 - 0.82 log d - 0.001611 Vs, (XIV-5)
where
Vs = Из = ’И3,
and the other symbols have the same meaning as in Eq. (XIV-3). Values
of the accuracy lives of U.S. Navy guns of various calibers computed
according to this formula agreed within about 15 percent on the
average with estimates made by the Naval Proving Ground, based on
firing experience. Values of N calculated from Eq. (XIV-5) were
arranged in the form of an alinement chart [Bur. Ord., 1939b] by
means of which the calculation can be carried out quickly with an
accuracy of about 2 percent.
128.	Kent1 s formula for the life of guns-^^/
The following formula for the life of guns, which is dis-
tinguished from the Navy formula in that it involves the maximum
pressure, was developed by Kent [1939]г
N = AdaKbPc,	(XIV-6) '
108/ See Sec. 130 for a comparison of this formula with others.
- 230 -
where N is the accuracy life in rounds, d is the caliber in inches,
k[= iH2] is the muzzle energy in foot pounds, P is the maximum
pressure in pounds per square inch, and A, a, b and c are empirical
constants. These constants were determined by the method of least
squares from data for a number of Navy guns. When the values thus
computed are used, the formula becomes
N = 10.26 x Ю1? d3«$7S	p-1 «761.	(XIV-7)
Kent used this formula to calculate the accuracy lives of a number
of Army guns and then compared the values so determined with those
given in the Ordnance Proof Manual [Ord. Dept., 1936]. The cal-
culated values were consistently lower than the latter estimates.
Kent [1939] suggested that ’’this discrepancy arises mainly from
failure to allow for the rounds fired with reduced charges in the
estimated lives of the guns given in the Proof Manual, ’*
129.	Other formulas for the life of guns
(a)	Jones1 formula?-—— One of the earliest attempts
to develop a formula for the life of guns was made by Jones [1911]
on the basis of an analysis of the heat transferred from the powder
to the bore surface in the region of the position of maximum pres-
sure. He proposed the relation,
A	(XIV-8)
V2 d(d- 2)p1‘7
108а/ See Sec. 130 for a comparison of this formula with
others.
- 231 - ,
where the symbols have the same moaning as in Eq. (XIV-6). Jones
proposed the value A s 1,2Ц x 10^ for guns firing cordite M.D.;
Kent [1939] has remarked that the French have used a value of A
that is 5>0 percent greater for guns firing nitrocellulose powder.
These values of the constant are for the purpose of giving an
estimate of the probable life before relining in peacetime, Jones
having suggested that the actual life of serviceability would be
30 to ЦО percent greater. Even the lower value of A, however, gives
high estimates of life, as is shown in Table XXVIII, Sec. 130.
(b)	Justrow* s formula. — As a result of a detailed considera-
tion of the many factors' that affect the life of guns, Justrow [1923,
Eq. 20] proposed the following formula for the number of shots that
can be fired from a gun before the initial muzzle velocity is de-
creased by 10 percent:
N = (xy/d2)(Av71)(G€/Ak),	(XIV-9)
where x is an empirical function of the maximum pressure, £ is an
empirical function of the caliber, d is the diameter of the bore,
A is a factor of proportionality for expressing the weight of the
projectile in terms of the cube of the caliber, V is the muzzle
velocity, and 1 is the length of the tube in calibers; G6 is propor-
tional to the tensile strength of the tube material and дек to that
of the driving band, but the exact physical significance of these
symbols was not stated.
Justrow published graphs for x — which varied from 0 to 1.2J? —
and for — which varied from 0 to 1.0 — but did not tell how they
- 232 -
were derived. He gave a table [Justrow, \-923, Table VI] showing
calculated values for the lives of guns of different calibers and
lengths, having different maximum pressures, velocities and
weights of projectiles; but he gave no indication of how closely
these values agreed with experience.
(c)	The formula of Lintes. — Another attempt to include
the physical properties of the metal of the tube as factors in the
life of a gun was made by Lintes [1935, Eq. (28)]. Adopting the
criterion that the end of life is characterized by a 10-percent loss
of muzzle velocity, he deduced that
N = A(^ Ao)(d2/K)(R2/e),	(XIV-10)
where A is a factor of proportionality, w/qo is the ratio of the
weight of charge to the initial surface of the charge, d is the
diameter of the bore, K[= isMV2'] is the kinetic energy of the projec-
tile, R(kg/mm2) is the elastic limit of the metal of the tube, and
e is its modulus of elasticity. Lintes found empirically that A
is 700 for bag guns and 350 for case guns; and since w/"l0 usually
is 0.5, the formula is simplified to N = 175 d2R2/Ke for case guns.
He stated that in rapid fire, N is reduced in the ratio no/n,
where n0 is the normal rate of fire and n is the increased rate.
The examples of the application of- this formula which Lintes cited
showed reasonably good agreement between the calculated and the
observed values for the length of life.
- 233 -
130» Comparison of estimates of lives of guns
The lives of a few typical unplated guns firing nitrocellulose
powder have been computed for the present report by Eqs. (XTV-5),
(XIV-7) and (XIV-8), with the results listed in Table XXVIII. The
Navy formula [Eq. (XTV-£)] was not intended to be used for calibers
smaller than 3-in.; and Jones formula [Eq. (XIV-8)] obviously cannot
be used- for small calibers, because of the term (d-2). Similar
calculations using Eqs. (XIV-?) and (XIV-10) were not made because
of lack of data concerning the physical properties of the gun
steels.
The remarkably close agreement between experience and the
estimates for the life of the Ц.7-in. gun T2 given by Eq. (XIV-5)
and (XIV-7) is probably a coincidence, inasmuch as the two equations
show systematic deviations from actual values for different calibers.
Both of them tend to give somewhat low estimates, those computed by
Kent's formula [Eq. (XIV-7)] being in general lower than those com-
puted by the Navy formula [Eq, (XIV-5)]. Except for the l5>3-mm,
1Ц-in. and 16-in. guns, the estimates by the Jones' formula
[Eq. (XIV-8)] are much too high.. 
All three formulas indicate the general inverse dependence of
the life of a gun on the muzzle energy. However, the exact functional
relation between them and the extent to which it is modified by other
factors are not adequately expressed by any of these formulas.
Table XXVIII. Calculated accuracy lives of guns.
Gun	Velocity V (ft/sec)	Pressure P (lb/in?)	Caliber d (in.)	Length 1 (calibers)	Proj.Wt. M (lb)	Muzzle Energy, E (ft lb)	Accuracy Life, N (rds)			
							Equation Number			Exp.*
							xiv-5	XIV-7	XIV-8	
Caliber . 50	2800	Ц8 000	0.5	72	0.101	1.2Ц x 10U	—	51 7Ц	—	8000
37-mm M1A2	2600	36 000	1.U57	53-5	1.3U	1.38 x 105	—	6161	—	3000 to 3500
75-mm M1897	1950	36 000	2.95	~ 3U.5	1Ц.6	8.67 x ю5	U365	31190	20850	10000
14.7-in. T2	3150	38 000	U-7	6o	5o.o	7.76 x Ю6	398	I4OO	1613	500 to 600
5-in./25 Mk X	2175	38 000	5.0	25	51.7	3.96 x 106	2203	1669	2862	2500
155-mm G.P.F.	2Ц00	28 000	6.1	38	95.8	8.62 x 106	1995	Ш52	2370	. I4OOO
8-in. Mk VI	2750	38 000	8.0	U5	261.8	3.09 x 107	518	226	507	—
8-in. Mk IX	2800	38 000	8.0	55	260.0	3.18 x 107	269	253	560	14OO
lU-in./50 Mk IV	2800	38 000	H4.O	5o	H4OO.O	1.71 x 108	230	91	II4O	175
16-in. M1919M3	2700	38 000	16.0	5o	23U0.O	2.67 x 108	166	77	12Ц	175
w This column lists the life based on experience, according to the following sources of information:
caliber .$0, Capt. 0. E. Balleisen, personal commtmication; 37-mm, Ord. Dept. [ 19U1]; 75-mm, Ord. Dept.
[1936 J; Ц.7-in., S. Feltman, personal communication; 5-in./25 Mk X, Bur. Ord. [19h2]; 155-mm, Weyher [1939]
8-in. Mk IX and ТЦ-in., Bur. Ord. [191|2]; 16-in., Ord. Dept. [1936].
- 235 -
CHAPTER XV. THEORIES OF THE MECHANISM OF EROSION
131.	The foregoing account of the erosion of guns reveals that it
is a complex phenomenon. The various theories of the mechanism of
егпяпрп''09/ are attempts to explain in specific terms the following
generalized description of that phenomenons during the firing of a
gun a physical or chemical agent, or a combination of such agents,
loosens some of the steel on the Surface of the bore and then either
the same or some other agent removes it from the bore. Whereas each
theory has emphasized the alleged effectiveness of some particular
agent or agents, the convincing evidence-adduced in partial confirma-
tion of each of them lends weight to the opinion, already expressed
by earlier writers [for instance, de Bruin and de Pauw, 1929;
Kosting, 1939a] that the true explanation of erosion must take
account of more than one causative factor.
In the present chapter!-^/ the several theories are classified
with respect to the agents proposed, in an attempt to summarize some
of the facts presented in the earlier chapters and to point out 
deficiencies in our knowledge that need to be supplied before the
mechanism of erosion will be understood. This classification is
most conveniently made with respect to the agents responsible for
109/ A convenient review of the principal theories was given
by de Bruin [1930]•
110/ At some time in the future it is intended to prepare a
more complete analysis of these theories, with consideration being
given to the additional information acquired in recent investiga-
tions of erosion.
- 236 -
loosening the material from the surface of the bore. After the
material has been loosened, it is considered to be either blown
out of the bore by the powder gases or else rubbed off the surface
of the bore by the rotating band.
132.	Melting of the bore surface
The quantity of heat liberated inside a gun is a major factor
in determining the amount of erosion, as is demonstrated by the fact
that in a given gun the amount of erosion is greatly increased either
by an increase in the weight of the powder charge or by the use of
the same weight of a powder having a higher heat of explosion. It
has not yet been possible to express quantitatively either how
much of the heat liberated inside a gun is absorbed by each portion '
of the surface of the bore or to what temperature that surface is
raised by the heat absorbed. Hence there is yet no proof that the
surface is melted — which is the simplest hypothesis to account
for the loosening of metal from the surface of the bore — for
raising the temperature of the bore surface may simply accelerate
some other change.
The hypothesis that the surface of the bore is melted has
usually been combined with the idea that the loosened material is
swept out of the bore by the powder gases. Considerable difference
of opinion, however, has arisen as to whether this supposed melting
of the surface and removal of the melted layer is performed by
small jets of gas escaping past the rotating band or by the main
stream of gas moving down the bore behind the projectile. As
- 237 -
mentioned previously (Sec. 11Ц), the gas leakage theory has had a
long history, beginning with Lanfroy [188$] and continuing with
Vieille [1901]> Yarnell [1910,], Bourgoin [1913] and Justrow [1923]»
Charbonnier [1908, 1922], Alger [1910] and Jones [1911]j among
others, opposed this point of view very strenuously.
Greaves, Abram and Rees [ 1929], who also considered that during
erosion a layer of molten metal is blown off the bore surface,
implied that this was done by the main stream o^ gas. They did not,
however, go as far as Charbonnier [1908, 1922] had gone in attributing
 ' \
erosion to a vena contracta effect of the stream of gas following the
projectile. Letang [1922] and also Justrow [1923] calculated that a
major part of the heating of the bore surface to its melting point
was caused by the heat resulting from the work of engraving the
rotating band.
Johnson [19Ц2] combined the action of both gas leakage and the
main stream of gas in his theory of erosion, according to which the
escape of gas past the band heats the skin surface of the bore almost
to the melting point before the projectile moves, so that after it
has moved, the main stream of gas is able to erode a short section
of the bore by fusion. Farther up the bore the surface is not
eroded by the main gas stream because it has not been subjected to
preheating by gas leaking past the band. This theory has the appeal
of a compromise, but it has no more basis in terms of observational
evidence than either of the separate theories relating to fusion of
the bore surface; as yet there is not even proof that the bore
surface reaches the melting’ point.
- 238
133.	Abrasion by unburned powder.
As part of his theory of the vena contracta, Charbonnier [1908,
1 922] suggested that some of the erosion is caused by the scouring
effect of unburned grains of powder which are swirled about by the
gases. It is admitted that the powder grains are hard enough to act
like a sand blast, but there is no experimental evidence that they
do so. Kent [19Ы] pointed out that the escape of gas from the
burning grains might form a cushion which would prevent violent con-
tact between the grains and the bore surface. He suggested that a
test of this idea might be obtained by comparing the rate of ero-
sion of a gun fired with strip powder with that of one fired with
grain powder of the same composition.
13h. Cracking of the bore surface
The severe thermal stresses developed on the surface of the
bore during the sudden heating followed by sudden cooling that
occurs during firing have been analyzed by Tschernoff [1913], by
Howe [1918], by de Sveshnikoff [1922] and by Justrow [1923] (see
Sec. 70). Tschernoff in particular considered these stresses
as the main cause of loosening material from the bore surface,
whereas Howe and Justrow attributed to them merely secondary in-
fluence. Similarly, Vieille [1901] had ascribed to the cracks
on the bore surface only a contributory effect that made leakage
possible.
- 239 -
«
139. Chemical reaction between the bore surface and the powder gases
Intimately related to the cracking of the surface of the bore
is the question of chemical reaction between the powder gases and' the
surface. Vieille [1901]} on the basis of a microscopic examination
by Osmond [1901 ] of an eroded gun, had concluded that the surfa.ce
layer of steel was hardened by carburization, and that it cracked
more readily because of this condition. The various investigations
by Fay [1916, 1 929], Howe [ 1918Wheeler [1 922], de Sveshnikoff
[1929]> Greaves, Abram and Rees [1929], Lester [1929a], Snair and
Wood [1938] and Kosting [1939a, 19hQ] on the possibilities of the
formation of a hardened layer on the surface of the bore by reaction
with the powder gases have been summarized in Secs. 79 to 79. In
spite of those extensive investigations, we are still ignorant of
the nature of the altered layer on the surface of the bore, and .
therefore we cannot say definitely how great an influence chemical
reaction between the bore surface and the powder gases may have on
erosion.
An entirely different type of chemical reaction was suggested
by Cole [19Ц1]. He assumed "that gases under extreme pressure and
high temperature approach the characteristics of dilute solutions"
and that they are highly ionized, both because of thermal agitation
and, because of collisions. The alloying elements in the steel
complete a galvanic couple, whereby iron is converted into an oxide
film when the highly ionized gas comes into contact with the sur-
face of the bore. An earlier suggestion of the possibility of
oxidation had been made by Crawford [1937] ? who supposed that the
- 2 ЦО -
surface of the bore is covered by an adsorbed ’’film of one or more
molecular layers of oxygen, which, when the surface reaches a
critical temperature, is released and forms an oxide with the sur-
face layer of the metal.'1 The layer of oxide, according to both
hypotheses, is swept away by the gases moving with high velocity.
136. Muzzle erosion
The foregoing discussion of causes of erosion has been
limited to erosion in the region of the forcing cone. The cause of
erosion at the muzzle is equally unknown. Three principal theories
have been advanced to account for it. According to the first, which
has already been mentioned (Sec. h7)j muzzle erosion is simply the
result of frictional wear between the projectile and the bore,
although why the erosion decreases progressively away from the muzzle
is not explained. This point of view seems to be current among
students of the subject in the U.S. Army today.
The other two theories explain muzzle erosion as caused by
the powder gases. Charbonnier [1^22] pointed out that his vena
contracta theory of erosion at the forcing cone applied equally well
to erosion at the muzzle, where another discontinuity in the gas
stream occurs. Thompson [1?Ц1], on the other hand, advanced the
theory that muzzle erosion is caused by the jet of high-velocity
gas that rushes through the annular orifice formed at the moment the
rotating band breaks contact with the bore.
The remarkable reduction of muzzle erosion in guns using the
R. B. system of rifling (Secs. 122 and 126) seems to discredit both
the theories of frictional wear and of the vena contracta effect.
- 2h! -
In the R. D. system [Naval Intell., 19Ц2] the grooves decrease
gradually in depth toward the muzzle, and for the last three calibers
of its length the bore is smooth. The original purpose of this
change was to erase the rifling marks from the rotating band in order
to decrease the air resistance of the projectile in flight. Limited
tests of guns rifled in this way, however, have given the unexpected
result of almost complete absence of muzzle erosion. Thus the modi-
fied 3.7-in. quick-firing gun mentioned in Secs. 122 and 126 showed
no erosion at the muzzle after 80 rounds, whereas the conventional
gun fired under similar conditions showed an increase of diameter
beginning about 27 calibers from the muzzle and increasing almost
linearly to a maximum of 0,018 in. at the muzzle.
137« Summary
The one single feature of the mechanism of erosion to which
all investigators have subscribed is that it is a dynamic phenomenon.
Erosion occurs only when the bore surface is attacked by hot powder
gases in motion, as was pointed out by Sir Andrew Noble [1906], one
of the earliest students of the subject. Therefore, in order to
achieve a true explanation of erosion, it will be necessary to under-
stand in detail the physico-chemical changes that the material of the
bore undergoes as it reacts with a rapidly changing environment
during firing.
2h3 -
BIBLIOGRAPHY AND AUTHOR INDEX—
for PART TWO
A. 0. [19U2a] (Sec. 101)
"Repair of guns by electrodeposition. Summary of positions,
March 31, 19Ц2," Adv. Council Sci. Res. Tech. Dev. to British
Ministry of Supply, A. C. 1965 (Apr. 16, 19h2).
A. C. [19U2b] (Sec. 101)
"Repair of worn-out gun barrels by electrodeposition. Note on
position on May 20, 19Ц2," Adv. Council Sci. Res. Tech. Dev. to
British Ministry of Supply, A. C. 217h.
Alger, P. R. [1910] (Sec. 11Ц, 132)
"Gun erosion," reprint U.S. Naval Institute Proc. 36, 697-705
(1910)5 Ordnance Dept. Library.
Altshuler, Bernard [ 19111 ] (Sec. 105b)
"Report on the firing test to determine the limits of accuracy
life of a h.7~in. gun T2," Aberdeen P. G., Ballistic Res. Lab.
Rept. No. 25Ц (Sept. 10, 19hl).
Ames, T. L. [1921] (Sec. 92)
"Preliminary report on erosion tests of Browning machine-gun
barrels. Rept. No. 9 — The manufacture, physical and chemical
properties of machine-gun barrels made of invar steel,"
Springfield Armory; manuscript (Feb. 8, 1921), 2 p.; Ordnance
Dept. Library.
Benson, A. E. [19U1] (Sec. 100)
Remarks at conference on gun erosion, Watertown Arsenal,
Watertown, Mass. (Oct. 15, 1911.1)- Report of conference,
Watertown ArseYial, p. 11.
Bihlman, V. W. [1921] (Sec. 71, 7Ц, 75, 77)
"Preliminary report on erosion of Browning machine-gun barrels.
Rept. No-. 8 — Metallographic examination after firing of
Browning machine-gun barrels made of twenty-one special steels,"
manuscript (Jan. 19, 1921), Ц p.; Ordnance Dept. Library.
Bone, W. A., D. M. Newitt and D. T. A. Townsend [1929] (Sec. 89c)
Gaseous combustion at high pressures, London: Longmans, Green
(1929), 396 p.
111/ The section number given on the same line as the author's
name refers to the present report.
- 2ЦЦ -
Bourgoin [1913] (Sec. 11Ц, 132)
Mem. artillerie navale 7, 3h3 (1913)-
Browne, C. A. [1939] (Sec. 73)
’•Charles Edward Munroe: 18Ц9“1938," J- Am. Chem. Soc. 61,
1301-1316 (1939).
Bruin, G. de [1930] (Sec. 131)
l,La poudre sans fumee et 1*erosion des bouches a feu. I.
Court apergu historique et critique du sujet," Communique
de la Ste. Anme^ "Fabrique Neerlandaises d’Explosifs" No. 10
(1930), 39 p. English translation by Lt. Col. Aiken Simons,
Mil. Sales Div., E. I. du Pont de Nemours and Co. (Mar. 1931),
Ц9 p.; Ordnance Dept. Library.
Bruin, G. de and P. F. de Pauw [1928 ] (Sec. Ю9)
’•La temperature de combustion de la poudre sans fumee en
fonction de sa composition chimique. II. Partie experi-
mentale" [See Moesveld, 1928, for Part I.] Communique de
la Ste. Anme. "Fabrique Neerlandaises d*Explosifs" No. 8
(1928); Ordnance Dept. Library.
Bruin, G. de and P. F. de Pauw [1929] (Sec. 131)
"La temperature de combustion de la poudre sans fumee en
fonction de sa composition chimique. III." Communique de
la Ste. Anme. "Fabrique Neerlandaises d'Explosifs" No. 9
(1929); Ordnance Dept. Library.
Bruin, G. de and P. F. de Pauw [1931] (Sec. 83,86,87,109,110c)
"La poudre sane fumee et 1'erosion des bouches a feu. II.
Partie experimentale," Communique de la Ste. Anme. "Fabrique
Neerlandaises d'Explosifs" No. 11 (1931), 27 p, English
translation by M. S. P., Mil. Intell. Div., War Department;
Ordnance Dept. Library.
Bur. Ord. (Navy Department)[1928] (Sec. 127)
"Erosion, a general formula for, in U.S. Naval guns," Memo.
from G. L. Schuyler to Chief of Bureau of Ordnance, 372-^/11/77
(Dec. 29, 1928).
Bur. Ord. (Navy Department) [1931] (Sec. 83, 87, 9hc)
"Erosion plug tests — relationship to gun erosion," Naval
Proving Ground letter to Chief of Bureau of Ordnance,
S72-U (9)/L3-2(2) (Mar. 30, 1931).
Bur. Ord. (Navy Department) [1933] (Sec. 127)
"Formula for life of guns," Section "K" Memo, to Chief of
Bureau of Ordnance, S72-h(22/39) (Nov. 20, 1933).
- 2Ц5 -
Bur. Ord. (Navy Department) [1938a] (Sec. 9hc)
’•Erosion plug tests *-summary of tests 1 929-31,dnd later,"
Naval Gun Factory letter S7h-1(3137)(K) (Feb, 10, 1938).'
Bur. Ord. (Navy Department) [1938b] (Sec. 98)
"Experimental firings of 1800- and 20OO-lb projectiles' in
1h-in. guns; partial report covering the firings scheduled
in 1h-in./ЗО-caliber Mark C gun, No. 110L2," Naval Proving
Ground letter to Chief of Bureau of Ordnance, S78-I(ЗЦ-Th-in.)
L5-2(B6h37) (Apr. 27, 1938).
Bur. Ord. (Navy Department) [1939a] (Sec. 98)
"Life of gun program with 1h-in./30-caliber Mark C gun, Nd. 110L2,"
Naval Proving Ground letter to Chief of Bureau of Ordnance,
S72-h(m-in.) (B86h7) (Mar. 31 , 1939).
Bur. Ord; (Navy Department) [1939b] (Sec. 127)
"Suggested modification for generalized erosion formula," Bureau
of Ordnance Memo., T11-3 (Sept. 29, 1939).
Bur. Ord. (Navy Department) [19h2] (Sec, 130)
"Table of estimated lives of U.S. naval guns," Washington, D.C.:
Bureau of Ordnance, O.D. No. h398 (Apr. 23, 19h2), Ц p.
Bur. Stand. [192ЦЬ] (Sec. 92)
"Report on Investigation of machine-gun barrels manufactured
from special steels," Bureau of Standards and Ordnance Department
joint investigation; manuscript (June ,192Ц), about 100 p.;
Ordnance Dept. -Library.	,
Burlot, E. [1923] (Sec. 89a)
"Note sur la mesure des resistances opposees par les metaux a
des deformations rapides. Application a la mesure des pressions
developpees en vas clos par la combustion de la poudre," Mem.
poudres 20, 233-322 (1923); Ch. Abs. 18, 2077.
Caldwell; F. R. and E. F. Fiock [19Ul] (Sec. 89c)
"Some factors influencing the performance of diaphragm indicators
of explosion pressures," J. Res. Bur. Standards 26, 173-96(19^1).
Charbonnier, P. [1908] (Sec. 132, 133)
Balistique interieurs, Paris: Doin(l908).
Charbonnier, P. [1922] (Sec, 11Ц, 132, 133, 136)
"La veine gazeuse," Mem. artillerie francaise 1_, 1001-11 (1922).
- 2Ц6
Cole, T. S. [19Ы] (Sec. 135)
"Electrochemical theory of erosion of gun barrels," manuscript
(no date), Ц p.; manuscript (no date), 2 p.; comments by
Ordnance officers; Ordnance Dept. Mail and Record Section,
File 0.0. Ц00.111/Ц161, T. S. Cole.
Crawford, D. J., Jr. [1937] (Sec. 135)
"The applicability of photography and spectroscopy to some
problems of interior ballistics," Watertown Arsenal Rept.
No. 122/9 (1937), 18 p. and bibliography, 5 p.
Cranz, C. [1926] (Sec. 102)
Lehrbuch der Hallistik, 3 vols., Berlin: Teubner (1913).
de Bruin, G. See: Bruin, G. de
de Sveshnikoff, W. W. See: Sveshnikoff, W. IV. de
Desmazi&res [1922] (Sec. 89a)
"Mesure des pressions absolues au moyen des crushers," Mem.
artillerie fran^aise 1_, 777-826(1922).
DuMond, J. W. M. [19U1] (Sec. 89c)
New equipment for measuring and recording the pressure of
powder gases in rocket chambers and the thrusts exerted by
blocked rockets, each as a function of time, NDRC Memos. A-28M
to A-30M (OSRD No. 30), bound as one (Oct. 9, 19L.1)•
Eckhardt, E. R. [1922] (Sec. 89b)
"A precision high-speed oscillograph camera," J. Franklin Inst.
19Ц, 1x9-67(1922).
Epstein, Samuel [1936] (Sec. 71)
The alloys of iron and carbon. Vol. I. Constitution, New York
and London: McGraw-Hill (1936).
Fay, Henry [1913] (Sec. 7U, 77)
"Tests of trepanned rings from 12-inch gun," Tests of metals,
Watertown Arsenal (1913)} p. 132-6 and 6 plates; also published
as Appendix II of Report of Chief of Ordnance (1913).
Fay, Henry [1916] (Sec. 70, 71, 73, 75, 135)
"Erosion of guns: the hardening of the surface," Bull. Am.
Inst. Mining Engrs. 56, 2237“51(1916); reprinted in Journal
U.S. Artillery h7, 392-ЦО5(1917)j abstracted in Iron Age 98,
1290-3.
- 2Ц7 - -
Fay, Henry [1921] (Sec. 76)
“Nitrogen and case-hardening," Chem. and Met. Engr. 2-Ц, 289-90
(1921).
Fay, Henry [1925] (Sec. 76,’ 135)
"The cause of the white layer," Army Ordnance 5, 798-9(1925).
Feltman, S. [1929] (Sec. 121)
"Effect of obturators and distance wadding," Report of Project
KW 366, Ordnance Dept. (Nov.16, 1929).
Fleming, J. P. [1918] (Sec. 103)
"Erosion tests of high silicon-chrome-vanadium steel in Lewis
aircraft automatic-rifle barrels," manuscript, Ordnance Dept.
(June, 1918); Ordnance Dept. Library.
Fleming, J, P. [1 91 9] (Sec.,97)
"Erosion in machine guns and automatic-rifle barrels," letter
to Major F. F. McIntosh, Technical Staff, Metallurgical Branch
(June 12, 1919)* h p. and bibliography, h p.j Ordnance Dept.
Library.
Goranson, R. W., Wm. Garten, Jr. and J. A. Crocker [19h2] (Sec. 89a)
The measurement of large transient stresses, NDRC Report А-Ц5
(OSRD No. Ц98) (Apr. 6, 19h2), 33 p. '
Grant, G. P. [19Ш ] (Sec. 103)
"Erosion of ,50-caliber machine-gun barrels. First report of
Ordnance Program 537h,” Aberdeen P. G. (June 30, 19hl), 220 p.;
Ordnance Dept. Library.
Graziani, M. [1928] (Sec. 76)
"Alterazioni dell1 aciaio dei tub! d'anima delle bouche da fuoco,"
Rivista d'Artiglieria e Genio Ц5, I4.OI4.(1 928).
Greaves, R. H., H. H. Abram and S. H. Rees [1929] (Sec. 65, 70, 71,
72, 73, 7h, 75, 8Ц, 85, 87, 93, 106, Ю7, 113, 117, 118, 132, 135 )
"Erosion of guns," J. Iron and Steel Inst. 119, 113-167(1929);
includes а Ц-р. bibliography.
Guion, J. L., H. G. Carter and N. L. Reed [1937] (Sec. 70)
"Miorographic and macrographic studies of a 1.1-in. Navy machine
gun No. 73, centrifugal casting C533," Watertown Arsenal Report
No. 3lh/533(Mar. 2, 1937).
Hardcastle, J. H. [190U] (Sec. '68)
"Remarks on rust, wear and erosion in gun barrels, with especial
reference to small arms," Proc. Roy. Artillery Inst. XXXI, No. 2
(July 190Ц).
- 2Ц8 -
Hatcher, J. L. [1920a] (Sec. 92)
"Report on test of 21 Browning machine-gun barrels of dif-
ferent steel compositions," manuscript, Springfield Armory
(Oct, 9, 1920), Ц p.; Ordnance Dept. Library.
Hatcher, J. L. [1920b] (Sec. 92)
"Report on test of Browning machine-gun barrels made of invar
steel," manuscript, Springfield Armory (Nov. 1920), 2 p.
Ordnance Dept. Library.
Hickman, C. N.,[1981] (Sec. 89a)
The use of copper balls for measuring pressures in combustion
chambers, NDRC Report A-21 (OSRD No'. 28) (Nov. 28, 198l), 9 p.
Howe, H. M. [1918] (Sec. 68, 70, 7b 75, 138, 135)
"The erosion of guns," Trans. Am. Inst. Min. Met. Engrs. 58,
, 513-96(1918).
Howorth, H. G. [19Ю] (Sec. 70)
"The cracking of inner tubes (carbon steel)," Research Dept.,
Woolwich; R. D. Report No. 11 (19Ю).
Inglis, N. P., and W. Andrews [1933] (Sec. 73)
"The effect on various steels of hydrogen at high pressures
and temperatures," J. Iron Steel Inst. 128, 383~8O8(1933)•
Jeansen, 0. F. [1936] (Sec. 102)
"A treatise on rifling of guns," Washington, D.C.: Bureau of
Ordnance, Navy Department (June 1936), 53 p.
Johnson, F.G. L. [1982] (Sec. 122, 132)
National Inventors Council Suggestion No. 527, consisting of:
(a) manuscripts, "Short outline of Commander Johnson's theory
of erosion" and "Description of the 'J* band" (liar. 19, 1982);
(b) Correspondence relative to the submission of this sug-
gestion.
Jones, Brymor [1982] (Sec. 72, 78, 75, 77) 
"The nitrogen content and constitution of the hard white layer
in eroded guns," Woolwich Research Dept, and University
College, Cardiff; extra-mural Rept. No. 8(Feb. 1982).
Jones, B.-, and H. E. Morgan [1932] (Sec. 77)
"Investigations into the nitrogen-hardening of steels,"
J. Iron Steel Inst. 21, 51(1932).
- 2Ц9 -
Jones, H. J. [1911 ] (Sec. 129a, 132)
’’The erosion of gun tubes and heat phenomena in the bore, of a
gun," Engineer 111, 29h,. .317, 380, 399(1911).
Justrow, Capt. [1923] (Sec. 129, 132, 13U)
"Theoretische Betrachtungen uber die Lebensdauer, usw.,"
Charlottenburg (1923); translation, Ordnance Dept. Library.
Karcher, J. C. [1922] (Sec. 89b)
"A piezoelectric method for instantaneous measurement of high
pressures," Sci. Papers of the Bureau of Standards (Aug. Ц, 1922),
8 p.
Kent, R. H. [1926] (Sec. 9hb)
"Closed bomb erosion test of bars of special steels," report for
Ordnance Program Ц7ЗЗ (Dec. 28, 1926), 2 p.
Kent, R. H. [1927] (Sec. 89b)
"Time-pressure records by a piezoelectric method," Ordnance Tech.
Notes No. 10(1927), 2I4. p.; Ordnance Dept., U.S.A.
Kent, R. H. [1938b] (Sec. 89b)
"The piezoelectric gage: its use in the measurement of gun-pres-
sures," Army Ordnance 18, 281-Ц(1938).
Kent, R. H. [1939] (Sec. 128, 129a)
"A formula for the accuracy life of a gun," Aberdeen P. G., 1
Ballistic Res. Lab. Rept.. No. 133(1939), 3 p.
Kent, R. H. [19Ы] (Sec. 133)
Remarks at conference on gun erosion, Watertown Arsenal,
Watertown, Mass. (Oct. 13, 19111). Report of conference,
Watertown Arsenal, p. 63.	,
Kent, R. H.,and A. H. Hodge [1939] (Sec. 89b)
"The use of the piezoelectric gage in the measurement of powder
pressures," Trans. Am. Soc. Meeh. Engrs. 6l, 197-2ОЦ(1939).
Keys, D. A. .[1921 ] (Sec. 89b)
"A piezoelectric method for measuring explosion pressures,"
Phil. Mag. Ц2, 1+73-88 (1921).
Kosting, P. R. [1931+] (Sec. 87, 91, 93)
"Gun erosion," Watertown Arsenal Rept. No. 731/2 (1 931+), 19 p.
and bibliography, 8 p.
- 25о -
Kosting, P. R. [1936] (Sec. 66)
"Pastilles: Partial Report I," Watertown Arsenal Rept, No.
731/1/1 (Jan. 15, 1936), 18 p.
Kosting, P. R. [1938] (Sec. 87)
"Erosion II. Plug erosion tests," Watertown Arsenal Rept.
No. 73l/37(June 15, 1938), 16 p.
Kosting, P. R. [1939a] (Sec. 79, 131, 135)
"A metallographic and diffraction study ,of erosion of guns,"
manuscript, 3 p.j Ordnance Dept. Library.
Kosting, P. R. [1939b] (Sec. 71, 7h, 78)
"The effect of service upon 75-mm gun M1897 No, 1537,"	//, , I
Watertown Arsenal Rept. No. 73T/hU(Aug. 29, 1939).	[ '
Kosting, P. R. [19Ц0] (Sec. 70, 71, 72, 7h, 78, 95, 135)
"37-mm Browning automatic gun M1, No.-1 barrel," Watertown
Arsenal Rept. JJo^JT34-/l;5(Oct. 17, 19h0), 16 p. 7
Kosting, P. R. [19Ц1] (Sec. 79)
Remarks at conference on gun erosion, Watertown Arsenal,
Watertown, Hass. (Oct. 15, 1 9h1)• Report of conference,
Watertown Arsenal, p. 19-
Kosting, P. R., H, G. Carter and N. L. Reed [1937] (Sec. 72)
"Machine-gun barrel No. 12 from Wright Field," Watertown
Arsenal Rept. No. 731/31(Sept. 28, 1937), 18 p.
Kosting, P. R. and R. E. Peterson [19h2] (Sec. 65, 70, 72)
"37-mm gun M1A2, No. 109," Watertown Arsenal Rept.
No. 731/59 (May 29, 19U2).
Lane, J. R. [1933] (Sec. 91, 96, 105a)
"Memorandum report on test of six 3-in. antiaircraft guns,
M1925 — radially expanded," report for Ordnance Program Ц615
(Apr., 2h, 1933), 6 p.
Lane, J. R. [1936] (Sec. 93)
"The influence of the melting point of the barrel material
on erosion, Project RB 152, firing with molybdenum barrels,"
Aberdeen P. G., Ballistic Res. Lab. Rept. No. 55 (July 16,
1936).
Lanfroy, A. [1885] (Sec. 11Ц, 132)
"Sur la cause des erosions dans l'Sme des bouches a feu,"
Mem. artillerie Marine 13, 173(1885).
-251 -
Langenberg, F. 0. [1916] (Sec. 71)
"The examination of rings from the.bore of 10-in. guns,. No. 21,
M1895, M1," Tests of metals, Watertovm Arsenal, ,(1916_),
pp. 105-108.
Lester, H. H. [1929a] (Sec. 71, 77, 135)
"The white layer in gun tubes and its relation to the case of
nitrided chromium-aluminum steel," Trans. Am. Soc. Steel
Treating 16, No. 5(1929).
Lester, H. H. [1929b] (Sec. 73, 77)
".50 caliber nitrided rifle barrel," Watertown Arsenal Rept.
No. 3hl(Jan. 21 , 1929), 16 p.
Lester, H. H. [1929c] (Sec. 99)
"Chrome plated . 30 caliber rifle barrels," Watertown Arsenal
Rept. No. 351(Nov.20, 19290, 22 p.
Letang, G. [1922] (Sec. 132)
"Sur l’usure des bouches a feu," Mem. artillerie francaise 1,
1013-1035(1922).	5
Lintes, J. [1935] (Sec, 125a, 129c)
"Etude critique sur l’usure des bouches a feu," Mem. artillerie
francaise 1Ц, 175-223(1935); translation in Ordnance Dept.
Library.
Manning, H. G. [1919] (Se'c. 125c)
"Loss of muzzle velocity due to erosion," Aberdeen P. G.; manu-
script (Feb. 10, 1919); Ordnance Dept. Library.
Marshall, Arthur [1917] (Sec. 106)
Explosives, London: Churchill; Philadelphia: Blakiston vol. I
and II, (ed, 2, 1917); 795 p.; vol. Ill, (1932), 286 p.
Marshall, Arthur [1920] (Sec, 73)
"The detonation of hollow charges," J. Soc. Chem. Ind. 39,
35t(192O).
Miller, H. W. [1920] (Sec. 66)
"Preliminary report on character, cause, rate and effect of the
various phenomena of the wear and erosion of guns," manuscript
(1920), 180 p.; Ordnance Dept. Library.
Miller, H. W. [1921] (Sec. 105d)
Railway artillery: a report on the characteristics, scope of
utility, etc., of railway artillery. Appendix I. "The German
long-range gun," p. 723“U5; Ordnance Dept. Doc. No. 2O3h;
Washington: Government Printing Office (1921).
- 252 -
Naumann, F. К. [1937] (Sec. 73)
"Einwirkung von -Wasserstoff unter hohem Druck auf unlegierten
Stahl," Stahl und Eisen 57, 889-899(1937)•
Naval Intell. [19h2] (Sec. 122, 136)
"'Probert' gun and projectile design," Report of Naval Attach^,
London, No. 838(Apr. 6, 19h2). This report contains a memo-
randum by Col. Probert, giving his interpretation of gun ero-
sion and suggesting a remedy.
Naval Ordnance [1912] (Sec. 6Ц)
"Erosion and life of guns," Naval Ordnance Pamphlet No. Ц12,
Washington! Government Printing Office (Oct. 1912).
Naval Ordnance [1926] (Sec. 105c)
Reports of special board on Naval Ordnance, Oct. 1 and 15,
1926, concerning 3”in./lO5-caliber gun. Quoted in letter from
Capt. G. L. Schuyler to J. S. Burlew, NDRC, Mar. 28, 19^2.
Noble, A. [1906] (Sec. 137)
"Researches on explosives, IV," Trans. Roy. Soc. (London)
2O6A, Ц$3(190б).
Noble, A. [1906 reprint] (Sec. 89a)
Artillery and explosives: essays and lectures written and de-
livered at various times, New York; Dutton(19^6), 5h8 p.
Noble, A. and F. Abel [187$] (Sec. 89a)
"Researches on explosives, I," Trans. Roy. Soc. (London)
(1875). Reprinted in Artillery and explosives (1906),
p. 99-230.
Norton, M. R. [1935] (Sec. 71)
"Metallographic polishing," Watertown Arsenal Report No. 1ЗО/З
(Aug. 19, 1935).
Norton, M. R. [1937] (Sec. 71)
"Metallographic polishing at Watertown Arsenal," Watertown
Arsenal Report No. 130/7 (Apr. 1937)»
0. В. P. [19Ma] (Sec. 108)
Ordnance Board (Great Britain), Proceedings No. 136О3 on
"Flashless propellants." The substance of this report is
found in Naval Intelligence Report, Serial 2681, Monograph
Index Guide No. Ц09-Ю0, a report from Naval Attach^ (London)
(Nov. 2h, 19Ы).
- 253 -
0. В. Р. [19t2a] (Sec. 101)
"Repair of bore by electro-deposition," O.B.P. No. 17,255
(Mar. 11, 19Ц2).
О. В. P. [19h2b] (Sec. 69)
"Use of tinfoil in ammunition of 37“ппп M.5 tank gun," O.B.P. No. .
17,508; 18,059; 18,060 (May 13-and June 19, 19Ц2).
0. В. P. [19U2c] (Sec.,108)
"Q.F. h0-mm guns. Relative lives with cordite W.T. and NH charges,"
O.B.P. No. 16,363 (Feb. 23, 19Ц2).
0. В. P. [19U2d] (Sec. 106, 108)
"Computation of charge values in E.F.C. Formula to' be used for
flashless and NH. Application to 6-pr. 7cwt.," O.B.P. No. I8,3h3
(July 6, 19U2).
0. В. P. [19U2e] (Sec. 101)
"Repair of bore by electro-deposition. Trial in Q.F. 3.7“ln.
barrels," O.B.P. No. 18,832 (Aug. 5, 19Ц2).
Ord. Dept. [1907] (Sec. 110a)
"Erosion tests of 6-pounder, using slow- and quick-burning powders,"
Ordnance programs 386, 398 and Ц10; Ordnance Department, Mail and
Record Section, File 0.0. 38961/5 and 0.0. 38961/17 (May 10, 1907)»
Ord. Dept. [1915] (Sec. 89a)
"Pressure gage outfits for determining pressures in cannon with
descriptions and instructions," Ordnance Pamphlet No. 1Ю9
(Rev. 1915), 10 p.
4s
Ord. Dept. [1920] (Sec. 125d)
"Erosion of guns," miscellaneous file, Ordnance Department;
3 vol., pages numbered consecutively (1920); Ordnance Dept. Library,
Ord. Dept. [1922c] (Sec. 105b)
"h.7-in. experimental gun, No. 808, fired in a program to develop
a higher grade of steel for gun construction," firing record of
this gun for rounds 22ЦЦ-2312, Ordnance Program Ц282 (June 19-23,
1922).
Ord. Dept. [1926] (Sec. 68)
"Test of gilding metal rotating bands," second report of Ordnance
Program Ц6Ц2 (Aug. 3, 1926).
- 23h -
Ord. Dept. [1929] (Sec. 99)
’’Test for determination of corrosion and erosion in chromium-
plated barrels for small arms,11 first report of Ordnance
Program 1911(Oct. 16, 1929).
Ord. Dept. [1932] (Sec. 89a)
"Small arms pressure gages (radial crusher type)," Eng.
Reprod. Plant, U.S.A.; Doc. No. 722? (Mar. 15, 1932).
Ord. Dept. [1936] (Sec. 89a, 10$, 128, 130)
Ordnance proof manual, Aberdeen P. G.; 1936 edition; issued
from Oct. 193б to Oct. 1938; looseleaf.
Ord. Dept. [1911] (Sec. 89a, Ю7, 119, 130)
"Endurance test of 37-mm gun M1A2 and powder," eleventh and
thirteenth reports of Ordnance Program Ц879 (Feb. 10-23, 1911).
Osmond, F. [1901] (Sec. 71, 75, 135)
"Note sur la trempe superficielle de l'acier soumis a 1*action
des explosifs," Hem. poudres salpetres 11, 211(1901).
Paquelier, R. [1929] (Sec. 69)
"Usure et desencuivrage des canons," Mem. artillerie francaise
8, 707(1929).
Peteval, J. E. [1905] (Sec. 89c)
"Pressure of explosion," Trans. Roy. Soc. (London) 203A,
33 7-98(1903).
Piantanida, E. [1922] (Sec. 76)
"Sulle alterazioni subite dall* acciaio dei tubi anima du
cannoni usurati," Rivista Karittima (1922); translation:
"Sur les alterations subies par l'acier de l'ame des canons uses,"
Mem. artillerie francaise 2, 1021(1923).
Piantanida, E. [1933] (Sec. 76)
"Le alterazioni dell* acciaio dei cannoni usurati dal tiro,"
Rivista Marittima 15 (1935); translation: "Les alterations de
l'acier des canons usee par le tir," Mem. artillerie francaise
17, 137-31(1938).
Ritchie, S. B. [1928] (Sec. 73, 91b)
"Development of a nonfragmenting gun steel, best suited for
cold-working," Watertown Arsenal Report No. 326 (June 6, 1928),
18 p.
- 255 -
Rockwell, S. P. [19191 (Sec. 95)
"Erosion in small arms," letter to Major McIntosh (Apr.. 18, 1919) t
3 p(; Ordnance Dept., Library.
Rosenhain W. and Beliew [1913] (Sec. 75)
"Erosion in gun tubes," Proc. Int. Assoc. Testing Materials II,
127(1913)» Discussion at 6th Congress of the Association in New
York on Sept. 3, 1912 of paper by Tschernoff [1913]«
Russell, H. 17. [19Ц1а] (Sec. 88)
"Erosion in gun-barrels," monthly reports of work under contract
with Watertown Arsenal; Battelle Memorial Institute; Feb. 19U1
to June 191x2, incl,; p. 1-h30.
Russell, H. W. [19Mb] (Sec. 88).
Remarks at conference on gun erosion, Watertown Arsenal, Watertown,
Mass. (Oct. 15, 19M). Report of conference, Watertown Arsenal,
p. 6.	.	.	.
Russell,-H. W. [19М] (Sec. 88, 99)
"Erosion in gun barrels," monthly reports on Contract 6183 with
Watertown Arsenal; first report, July 31, 19Ц2; Battelle Memorial
Institute; p. 1-17.
Sauveur, Albert [1935] (Sec. 75)
The metallography and heat treatment of iron and steel, ed. Ц,
Cambridge, Mass.: The University Press (1938)* 531 p.
Schwinning, W. [193h] (Sec. 102)
Konstruktion und Werkstoff der Geschutzrohre und Gewehrlattfe,
Berlin; VDI-Verlag GMBH(193M, 167 p.
Sharpe, P. В. [19Ц2] (Sec. 111, 112)
Complete guide to handloading, New York and London: Funk and
Wagnalls(l9h2), U65 p. and supplement, 72 p.
Shumate, P. W. [1938] (Sec. 71, 73, 7h)
"Properties of nitrided gun steels," thesis (M.S.), Massachusetts
Institute of Technology (1938); Watertown Arsenal Report No. 326/2,
33 p.
Siwy, P. [1908] (Sec. 6Ц)
“Die Abnutzung der Geschutze und deren Ursachen," Z. ges. Schiess u.
Sprengstoffw. 3* h2,66(1908).
Snair, W. H., and W. P. Wood [1939] (Sec. 72, 73, 77, 135)
"The white layer structure in the erosion of machine-gun barrels,"
Trans. Am. Soc. Metals 27, 608-21;(1939) •
- 256 -
Stefanides, V. See: Snair and Wood [1939) p. 621].
Sveshnikoff, IV. IV. de [1921a] (Sec. yO, 72, 73)
'•Some factors affecting the life of machine-gun barrels,4
Bureau of Standards Technical Papers No. 191(1921), 27 p«
Sveshnikoff, IV. IV. de [1921b] (Sec.. 73)
’’Life of machine-gun barrels. Part I. Abrasive action of
bullet and gases,'1 Army Ordnance 2, 16l (1921).
Sveshnikoff, IV. IV. de [1922] (Sec. 70, 97, 13k)
’’Life of machine-gun barrels. Part II. Cracking of the sur-
face of the bore,'1 Army Ordnance 2, 3011(1922).
Sveshnikoff, IV. IV. de [1925] (Sec. 71, 711, 76, 77, 135)
"Carburization as a factor in erosion of machine-gun barrels,"
Arm-у Ordnance 5, 7911(1925).
Sveshnikoff, IV. IV. de [1933] (Sec. 61i, 70)
"Data on some special steels for machine-gun barrels," Am. Soc.
for Metals 21_, 652-62(1933).
Sveshnikoff, IV. IV* de, and H. E. Haring [19211] (Sec. 101)
"Electroplating worn machine-gun barrels," Army Ordnance 5,
503-11, 51111(1921).
Thompson, L. T. E* [19111] (Sec. 136)
Reply to proposal for elimination of leakage past rotating
band, letter to P. 17. Bridgman, Harvard University (June 26,
1 9111).
Thomson, J. J, [1919] (Sec. 89b)
"Piezoelectricity and its applications," report of a lecture
delivered on Apr. 11 at the Royal Institution, Engineering
Ю7, 5113(1919).
Tolch, N. A. [1935] (Sec. 10Ц, Ю7)
"The rate of erosion of the Browning caliber .30 tank type
machine gun M1919 as dependent on the temperature of the gun
and other factors," Aberdeen P. G., Ballistic Res. Lab.
Rept. No. 13(July 8, 1935), 21 p.
Tolch, N. A. [1936a] (Sec. 67, ЮЗ)
"On heating effects and endurance properties of the 105-mm
antiaircraft gun M1 as determined by rapid fire tests,"
Aberdeen P. G., Ballistic Res. Lab. Rept. No. 35(Feb. 12,
1936), 16 p.
- 237 -
Tschernoff, D. К. [1913] (Sec. 70, 13h)
"Erosion of gun tubes," Proc. Int. Assoc. Testing Materials IT,
121-2(1913)- Written discussion read to sixth Congress of the
Association in New York on Sept, 3, 1912 by Capt. Beliew, after
paper on "The effect of high temperatures on, the physical
properties of some alloys" by I, H. Bregowsky and L. W. Spring.,
Vieille, P.. [1901] (Sec. 76, 8Ц, 83, 9ha, 110, 11Ц, 132, 13h, 133)
"Etude sur les phenomenes d'erosion produits par les explosifs,"
Mem. poudres salpetres 1J_, 137~21 9(1 901).
Vieille, P. [1906] (Sec. 89a)
["Arrangement of crusher gages in measurement of explosion pres-
sure,"] Comptes Rendus 1ЦЗ, 1218(1906).
Vincent, T. K. [1937] (Sec..99)
"Development of chrome-plating of guns," Aberdeen P. G.,
Ballistic Res. Lab. Rept. No. 87(Nov. 1937), 38 p.
Walther, H. H. [1938] (Sec. 73)
"Heat checks in brake drums," Brake Service (Aug. 1938).
Webster, A. G., and L. T. E. Thompson [1919] (Sec. 89c)
"A new instrument for measuring pressures in a gun," Proc. Natl.
Acad. Sci. 3, 239(1919).
Weyher, T. A. [1939] (Sec. 60, 61, 63, 123d, 130)
"Tests- to determine limits of accuracy life of 133-mm guns, G,P.F.,"
report on Ordnance Program 3h!2; Aberdeen P. G. (July 10, 1939).
Wheeler, H. E., [1922] (Sec. 73, 77, 133)
"Nitrogen in steel and the erosion of guns," Trans. Am. Inst.
Min. Het. Engrs. 67, 237“3O6, discussion 306-16(1922).
Wheeler, H. E. [1923] (Sec. 77)
"The nitrogen theory of erosion," Army Ordnance 3, 800(1923).
Whelen, Townseiji [-1930] (Sec. 99)
"Erosion test of caliber .30 chromiurf-plated machine-gun barrels,"
Springfield Armory (Jan. 29, 1930), Ц p.; Ordnance Dept. Library.
Wulff, John [19M ] (Sec. 97)
"Surface finish and structure," Metals Technology(l 9Ц1)'.
Yarnell, H. E. [1910] (Sec. 11Ц, 113, 132)  '
"Gun erosion," J. Am. Soc. Naval Engrs. 22, 33U(191O); Journal
U.S. Artillery ЗЦ, 181(1910).	'
- 259 -
112/
SUBJECT INDEX
for PARTS ONE AND TWO
Accuracy life, 10h.
See also Life of guns.
Adiabatic flame temperature,
36, 38, ЦО, Ц1, 109, 110(c),
VII, III,
Advance of forcing cone, 63,
125(d).,
Alloy steels, tests of, 92,
XXII, XXIII.
Altered layer
on bore surface, 71—79, 107,
13^
on erosion vent plugs, 73,
9h(b);
hardness of, 7U, XIX;
theories concerning, 75-77,
79;
thickness of, 72, 9U(b),
XVIII;
on various steel surfaces,
73, 117, 118. ••
Ammonia, action on steel of,
73.
Ammonia fumes, 25.
Ammunition, types of, 20, 21.
Artillery, 5.•
Austempering, XX.
Austenite, 75, 77, XX.
Autofrettage, 6.
Bag gun, 18, 21, 60, 118,
125(c).
Bainite, XX.
Ballistic force, Ц0.
Ballistics, interior, 29-58,
Ballistite, 26, 9h, XII,
Band, see Rotating band.
Band slope, 10.
Barium nitrate, 25, VI(A),
Barrels, machine-gun
of alloy steel, 92;
of nonferrous metal, 93.
Battelle Memorial Institute
erosion tests, 88.
Bell muzzle, 6.
Beryllium-copper, gun barrels
of, 93.
Black powder, 2Ц, 28, 33, 106,
VIII.
Boat-tail, 17.
Bore
contraction of, 56;
diameter of, 2, 55, 60,
125(c), I;
dilation of, 55.
Bore surface
chemical reaction of, with
powder gases, 135;
cracking of, 70, 78, 79,
107, 113, Uh, 13Ц, 135;
effect of, on erosion, 97;
heating of, Ц7, 51, 53, 5U,
56, 132, XIII;
lubrication of, 111-113-
Bore-sear'cher, 1I4.
112/ Arabic numerals refer to sections; Roman numerals, to
tables.
- 2.60 -
Boroscope, 1Ц,
Bourrelet
definition of, 17;
dimensions of, I,
Built-up guns, 6, 96, I.
Bullets, 17, 111, 112, 120.
Burning constant, 30.
Burning, rate of, 22, 23,
29-31, UU.
Burst, length of, effect on
erosion of, 103.
Caliber
definition of, 5;
variation of erosion with,
62, 6Ц, XVII.
Cannelure, 17, 18, 111, 122,
Cannon, 3.
Carbamite, 27, VI(B).
Carburization, 73-77, 133.
Cartridge case, 20.
Case gun, 18, 21, 60, 118,
123(d), 123(e).
\
Cementation, as ‘cause of
altered layer, 73-77, 133.
Cementite, 73, XX,
Centering cylinder, 10, 60.
Centralite, 27.
Chalk, VI(B).
Chamber, 2, 12, 13, 60, 73, I.
Chamber rear slope, 12.
Chamber slope, 10.
Chambrage, 12, 13. '
Charge, in various guns, I,
Chrome plating of guns,
98-100.
Chrome-plated erosion vent
plug, XXV(B).
Chronograph, Ц9.
Chronoscope, Ц8,
Closed-chamber experiments,
36-39, 30, 80,
Cold-worked guns, 6, 96, I,
Cold-working as cause of
altered layer, 73.
Combustion
heat of, 32, VII;
products of, 33-33, 39, IX,
X, XII.
Compression slope, 10.
Contraction of bore, 36,
Cooling
of machine-gun barrel, 31;
of closed chamber, 37, 38.
Copper gun barrel, 93.
Copper pressure-gage cylinder
89(a).
Copper rotating band, 18,
Copper vent plug, XXIV,
Coppering, 18, 60, 67-70, 113
"Coppers," 89(a).
Cordites, various, 26,
106-108, VI(B), VII, X, XI.
Cost of firing tests, XXI.
- 261
Govoluma, 37» 38.
Cracking
of bore surface, 70, 78, '79,
107, 113, 13U, 135;
of chamber surface, \73«
Cryolite, VI(B).
Decoppering, 25, 69.
Density of loading, 32, 37, I.
Dibutylphthalate, 25, Vl(A),
VII,
Dilation of tube, 55.
Dinitrotoluene, 2.5, VI(A),
VI’I.
Diphenylamine, 27, VI(A), VII,
Dispersion, 18, 82, 125(b).
Driving band, see Rotating , .
band.
Ductility of gun steel, 15.
Economic life of a gun,. 105(b),
125(f);
Seo also Life of guns.
Efficiency of a gun, Ц9.
Elastic limit of gun steel, 16.
Electric arc, altered layer
produced by, 73.
Elongation of gun steel, 15, .
XXII(C).
Energy, muzzle, Ц9, 52, XV;
distribution of, 52, XV;
loss of, 125(a)»
Enlargement'
of bore, 60-62, 125(b), 12.7,
XVI;
of cracks by copper, 68, 70.
Equilibrium, during burping of
powder, Ц2,
Equivalent service round, 12Ц,
Erosion curves, 61,
Erosion
definition of, 2., 137;
dissymmetry of, 60;
of drilled shot, 117;
effects of, see Forcing
cone, advance of; Life
of guns; Muzzle velocity,
loss of; Rotating band,
stripping of.
factors influencing, 81,
102, 130;
chamber design, 13;
chemical composition of
gun tube, 90-9U;
chemical reaction, 73,
75-77, 7.9, 135;
chrome plating, 98-100;
coppering, 68;
cold-working of tube,
96; ’
fire, continuous, 103;
gas leakage, 18, 11Ц;
heat, 132;
lubrication of bore,
111-113;
melting point of metal,
93, 9h(a), XXIV;
muzzle energy, 130;
muzzle velocity, 105;
physical properties of
gun tube, 90, 92;
pressure, 110;
propellant, 2Ц, 106-109;
rate of fire,103;
rifling design, 9, 119,
126, 136;
rotating band, 19, 131,
132;
stress concentrations,
9;
surface of bore, 97;
temperature, 10Ц, 109,
110(c);
turbulence, 13, 86;
velocity, 105;
weight of projectile, 105.
muzzle, 2, U7, 60, 72, 98, 136;
- 262 -
Er о s i on<—continued
tests of, see Erosion,
factors influencing;
Firing tests; Laboratory-
erosion gun; Vent plug
tests;
theories of, 75-79, 1Ш,
131-135.
Expans ion
of bore, 70, 13h;
of powder gases, 50;
radial, 96;
thermal, of gun steel,
XXII(B).
Explosives, high and low, 22»
Explos ion
heat of, 32, hl, VII;
products of, see Combustion,
products of.
Explosion pressure, 37»
Explosion, temperature, 36,
38, hO, Ц1, Ю9, 110(c),
VII, XII.
Fterrite, 75, 77, XX.
Fire, continuous, effect of,
on rate of erosion, 103.
Firing tests, 81-83, 92, 99,
105, XXIII.
Flashless propellants, 25,
108, VI(A), VI(B), VII, IX.
Forcing cone, 10, 126;
advance of, 63, 119, 125(d),
XVI.
Forcing resistance, Ц6.
Fouling, see Coppering.
Free run-up, 125(d).
Friction, bore, 19, h6, h7,
53, 136.
Fringing, 18.
Gages, pressure, 89.
Gas checks, 20, 121, 126,
Gas leakage
experiments on, 116-119;
theory of erosion by, 18,
110, 11U-122, 126, 132.
Gas reactions at high tempera-
tures, 38-Ц2,
Gas-washing theory of erosion,
93, 132.
Gases, powder, composition and
temperature of, 33-36, 38-Ц1,
5o, 135, VITI-XII.
Gilding metal rotating bands,
18, 68.
Granulation, 23, 31, 110(a).
Graphite, as bore lubricant,
111-113.
Graphite glazing on powder,
25, VI(A)„
Grooves, 8, 70, I;
erosion of, 60, 93, 105(a),
105(b), 107, 11Ц.
Gun
built-up, 6, 9б>, I;
case, 21, 60;
chrome-plated, 98, 99;
cold-worked, 6, 96, I;
definition of, 5;
laboratory erosion, 88;
nickel-plated, 101;
radially expanded, 6, 96, I;
tapered bore, 7;
wire-wound, 6, I.
Guns,- see also Supplementary
index of guns by calibers;
classification of, 5, I;
construction of, 6;
dimensions of, I,
- 263
Gunpowder, see Black powder.
Hard layer, hardened layer,
hardened skin, 71J
See also Altered layer.
Hardness, of altered layer,
7h, XIX;
of gun barrels, XXII(C).
Heat
absorbed by bore surface,
51, 75, 132, XIII;
of combustion, 32, VII;
of explosion, 32, VII;
of friction, 53.
Heat capacity of powder gases,
. u1, U2.	• . • .
Heat checking, 70, 93»
Heat flow in gun, 5h»
Howitzer, definition of, 5.
Hypervelocity guns, 3, 105(c),
112.
Hydrogen, effect on steel of,
73.
Igniter charge, 28, 31.
Inconel vent plug test, XXV(B),
Inclusions in steel, 78'.
Interior ballistics, 29-58.
Invar gun barrels, 92.
Ionization of powder gases,
135.
Iron, alpha and gamma, ?5, 77,
79.
"J" band, 122.
Jacket of bullet, 17'.
Keyhole, 82, 92, 125(e)*
Lands, 8, 9, 70, I;
erosion of, 60, 93, 105(a),
105(b), 107, 11Ц.
Length of gun, 105, I.
Life of guns, 123-130;
criteria for, 125;
effect of muzzle velocity on,
3, 105, XXVII;
formulas for, 127-130;
of special materials, 92.,
93, 98-101;
of various calibers, XXVII,
XXVIII.
Life of machine-gun barrels,
92, 10I1, 107, XXIII, XXVI.
Liner, loose, 6.
Lubrication of bore, 111-113»
Martensite, 75-77, 79, XX.
Materials for gun tubes, tests
of
by erosion vent plugs, 9I1;
by firing, 92, 93, 99;
by laboratory erosion gun,
88,.
Melting of bore surface, 132.
Melting point, relation of, to
erosion, 93, 911(a), XXIV.
Metal, weight of lost during
erosion, 6I1, XXIV.
Metals, pure, erosion resist-
ance of, 9h(a).
Methane, formation of, in
powder gases, 39, VIII, X, XI.
- 26Ц -
Mineral jelly- in cordite, 26,
27, VI(B).
Molybdenum liner, 93.
Monel metal
gun barrel of, 93;
vent plug test of, XXV (B).
Mortar, definition of,
Munroe effect, compared with
erosion, 73.
"Mushroom pad" obturator, 20.
Muzzle energy, Ц9, 128-130,
XV, XXVIII.
Muzzle erosion, 2, Ц7, 60, 72,
98, 136.
Muzzle velocity, h-9, 99, 100,
105, 127-129, I, XXVII,
XXVIII; see also Velocity,
muzzle»
Nickel-plated guns, 101.
Nickel steel for guns, 13, 91,
II, XXII, XXIII.
Nitralloy, vent plug test of,
XXV (B).
Nitride theory of erosion, 79.
Nitrocellulose, see Powder,
nitrocellulose.
Nitroglycerin, 22, 2Ц, 26,
106, 107, Vl(A), VI(B), VII,
X.
Nitrogen in altered layer, 77.
Nitroguanidine, 23, 108, VI(B).
Obturation of breech, 20.
Obturation of .bore, see Gas
leakage.
Ogive, definition of, 17.
Origin of rifling, definition
of, 11.
Paris gun, 103(d).
Pastilles, 66.
Pearlite, 73, XX,
Penetration of armor plate, 3.
Perforation of powder grains,
23.
Picrite, 2.3, 108, VI(B).
Plug gage, 63.
Potassium nitrate, 23, VI(A).
Potassium sulfate, 23, VI(A),
VI(B).
Powder
American, 23, 107, 108,
VI(A);
black, see Black powder;
British, 26, 108, VI(B);
burning of, 29-Ц2;
chemical composition of, 2Ц,
23, 26, VI(A), VI(B), VII,
X;
double-base, 2Ц, 107, 119;
aee also Cordites, various;
effect of type of, on rate
of erosion, 8Ц, 106-108,
XXVI;
energy distribution of, 32,
XV;
flashless, 23, 108, VI(A);
VI(В), IX;
FNH, 23, 27, VI(A), VI(B),
VII, IX;
forms of, 23;
ignition of, 30;
- 265 -
Powder—continued
NH, 25, 2?, VI(A), VI(B);
nitrocellulose, 22, 2Ц, 25,
26, 106, 107-109, VI(A),
VI(В), VII, X; products
of combustion of, 3U, IX,
X, XII;
pressure of, 29, I;
propellent, 2, 22-26, VI(A),
VI(B);
pyro, 25, 27, VI(A);
quickness of, 31;
single-base, 21;, 1Q7, 119;
smokeless, 2Ц;
stability of, 27;
unburned, 66, 133.
Powder chamber, see. Chamber,
Powder gases, see Gases,
powder,
Powder grain, dimensions of,
23 .
Powder potential, 32.
Pressure
decrease of, with erosion,
105(a), 105(b)•>
effect of, on erosion, 105,
110;
explosion, 37;
maximum, position of pro-
jectile at, Ц5;
muszle, 15;
starting, 18;
in various guns^ I,
Pressure gages, 89,
Pressure-time curves, ЦЦ.
Pressure waves, 31.
Primers, 28,
Probability of hitting an air-
plane, 3, 105(b).
"Probert" rifling, 122, 126,
136.
Projectiles, 2, 17-21, Ц3, 105,
113, I, V;
See also Bullets,
Proof stress, 16,
Propellant, see Powder,
Proportional limit, 16.
Proportional method, 16.
R, D, system of rifling, 122,
126, 136.
Radial expans ion, 6.
Range of-gun, decreased by
erosion, 2, 125(b).
Rapid fire, effect of, on ।
erosion, 103, Ю1;,
Resistance, forcing, 18, Ц6,
126, 132.
Rifling
depth of, I;
design of, 8, 9, 122, 126,
136;
length of, 10, I;
twist of, 8, 9, I.
Rotating band
composition of, 18j
design of, 10, 17, 18, 122,
126;
dimensions of, 18, I;
effect of, on erosion, 19> 119,
131, 132; on gas leakage,
1111.
engraving of, 18, Ц6, 126,
132;
erosion of, Till, 117, 118;
stripping of, 105(b), 125(e);
See also Friction, bore.
Rounds, variation of erosion
with number of, 61,
- 266 -
Scoring, 6$, 113, 117*
Service round, 12Ц.
Shot start pressure, 18,
Ц6, 126, 132.
Small arras, 3, 99, 100.
Solder as decoppering
agent, 69.
Solvents, powder, 2Ц.
Sorbite, 73, 93, XX.
Stabilizers, 23-27.
Star gage, Th, 6O-61, 6Ц,
99, XXII, XXIII.
Steel
alloy, 92, 9h(b), 9h(c),
XXV;
gun, composition of, 13,
92, II, III, IV,
XXII(A); heat treat-
ment of, 1.3, 92,
XXII(C); specifications
for, 13; thermal trans-
formation of, 92,
XXII(B); tensile
properties of, 13, 16,
92, 9h(b), XXII(C);
tests of, 92, 9h(b),
9h(c), XXIII, XXV?A),
XXVfB);
microstructural con-
stituents of, 73, 77,
93, XX.
Strength of gun tube 6,
70.
Stress on gun tube, 6,
33, 37, £8.
Stress concentrations,
effect of, on erosion, 9.
Surface of eroded bore,
70-79.
Temperature
of barrel, 31, 3h, ЮЗ, 10Ц,
XIII, XIV, XXVI;
of bore surface, 3h, 132;
of explosion, 36, 38, Ц0,
Ы, 109, 110(c), VII,
XII;
of powder gases, 38, Ц0,
Ы, vii, хи.
Tensile properties of gun
steels, see Steel, tensile
properties.
Tensile strength, 16, 103-
Time of flight, 3.
Tin, 23, VI(A).
Tinfoil, use of, in de- .
coppering, 69.
Tin oxide, 23, VI(A).
Tip, definition of, 82.
Transformation points of
steel, 92, XX, XXII(B).
Travel of projectile, h3, I.
Trinitrotoluene, 22.
Troostite, 71, 73, 76,
XVIII, XX.
Tube, 2, 6, I;
heating of, during firing,
h7, £l-5h, 36, 132,
XIII, XV;
reaction of, to firing,
31, 33-37.
Tumbling, 82, 123(e).
- 267 -
Tungsten steels, XXII,
XXIII, XXV(B).
Turbulence, '-13, 86».
Twist of-rifling-, 8, 9, I.
. ' г . . 
Vaseline., used in cordite,
26, 27, VI(B).
Velocity, muzzle, Ц9, 99,
- 100, 103, 127-129, I,
XXVII, XXVIII;
effect'of coppering
on, 67;
effect of, on ero-
. sion, 3, 103;
increase of, in
chrome-plated gun,
100;
loss of, 99, 100, 101 ,
103(a), 103(b),
123(a), 123(c),
123(d), 126;
loss of, by erosion,
99, 103(a), 103(b),
123(a), 123(c),
123(d), 126.
"Vena contracta,” theory
of erosion by, 132.
Vent, effect of sifce of, on
erosion, 83(a), 83(b).
Vent plug
altered layer of', 73, 9h(b);
effect of turbulence on,
13, 86.
Vent plug tests, 80, 8^-87,
9Ц, Ю9, 110(c), 113, XXIV,
XXV(A), XXV(Bj.
Wad, wax,-112.
Warming round, 12Ц.
Water-gas reaction, 39rh1, 30.
Wear, frictional, 2, h7, 136.
Web thickness, 23, 31»
Weight of metal lost by ero-
sion, 6Ц, 9h(b), XXIV, XXV.
White layer, see Altered layer.
Yaw, 82;
See also- Keyhole.
Yield-point, 16.
Yield strength, 13, 16.
SUPPLEMENTARY INDEX OF GUNS BY CALIBER
.30-caliber machine-gun
altered layer of, 72;
area under erosion curve
of, 6Ц;
chrome-plated, 99;
cost of firing to de-
struction, 83, XXI;
dimensions, I;
heating of barrel, 31,
l0i|, XIII, XIV, XXVI;
life of, 103, ЮЦ, 127,
..XXVI;'
partially chrome-plated,
100;
purpose of, I(notes).
,.30-caliber machine-gun
dimensions, I;
distribution of energy in,
XV;
heating of barrel, 31,
103,. XIII, XIV;
life, 123(a), XXVIII;
purpose, I(notes).
1.1-inch Navy gun
cracking of surface of
70.
IF1ED
- 268 -
37 gun
altered layer in, 72, 7h;
bore of, photograph of,
70;
chrome-plated barb of,
99;
cost of firing to de-
struction, 83? XXI;
cracking of surface
of, 70;
dimensions, J;
erosion of, 6l, 62, 107,
119, XVII;
forcing cone in,
advance of, 119;
heat of friction in,
£3;
life, XXVIII;
purpose, I(notes);
scoring of, 65.
90-mm gun
dimensions, I;
purpose, I(notes).
3.7-in. gun
loose liners for, 6;
nickel-plated, 101;
R. D. system of rifling in,
122, 126, 136.
105-mm gun
altered layer of, 7h;
ammunition, semifixed, 21;
dimensions, I;
erosion of, 103;
heating of tube, 51, 5U,
55, XIII, XIV;
purpose, I(notes).
75-mm gun
altered layer in,
7h, 79;
dimensions, I;
heating of tube of,
5h, XIII, XIV;
life, XXVII, XXVIII;
pastilles in, 66;
pressure-time curve,
Uh;
purpose, I(notes).
3-in. gun
bore surface of, photo-
graphs of, 71;
chrome-plated liners of,
99;
dimensions, I;
distribution of energy
in, XV;
erosion of, 60, 61,
105(a), 105(c),
XVII;
heating of tube of,
51, XIII, XIV;
life, XXVII;
loose liner for, 6;
pressure-time curve, ЦЦ;
purpose, I(notes).
U. 5-in. gun
eroded surface of, 107;
loose liner for, 6;
nickel-plated, 101.
U.7-in. gun
ammunition, semifixed, for, 21;
chambrage of, 12;
dimensions, I;
erosion of, 105(b);
life, 125(f), 130, XXVIII;
purpose, I~(notes).
5-in. gun
ammunition, semifixed, for,
21;
life, XXVIII;
6-in. gun
ammunition, semifixed, for,
21.
6-in, howitzer
eroded surface of,
107.
UNCLASS
155-пип gun
cost of firing to
destruction, 83, XXI;
dimensions, I;
erosion of, per round,
60, 61, 6Ц, XVII;
unsymmetrical, 60;
forcing cone of, advance
of, 63, 125(d),
XVI;
life, 125(f), 130,
XXVIII;
pressure-time curve,
hU;
purpose, I(notes);
weight of metal lost
in firing, 6Ц.
l55~ram howitzer
pastilles in, 66.
8-in. gun
dimensions, I;
erpsion of, XVII;
life, 125(b), XXVIII;
purpose, ifnotes).
12-in. gun
altered layer in, hardness of,
73, XIX;
cracking of surface of, 70;
effect of design of rifling on
erosion, 102;
weight of metal lost per round,
6Ц.
1h-in. gun
chrome-plated, 98;
cracking of surface of, 70;
dimensions, I;
erosion of, 61, XVII;
life, 125(c), 130, XXVIII;
purpose, l(notes).
16-in. gun
altered layer in, 7Ц;
cost of firing to destruction,
83, XXI;
dimensions, I;
erosion of, 62, XVII; .
life, 130, XXVIII; '	'
purpose, I(notes).