Hugh Chisholm.

The Encyclopædia britannica; a dictionary of arts, sciences, literature and general information (Volume v. 20) online

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each hank of 500 or 600 yds. of wire. Great importance is attached
to the absence of scale from the wire when it is being drawn, and,'
after pickling, the rolled bar and wire are treated with lime or some'
similar substance to facilitate the drawing. The tests for the
finished wire are as follows: it has to stand a tensile stress of from'
90 to no tons per square inch of section, and a test for ductility^
in which a short length of wire is twisted a considerable number of
turns in one direction, then unwound and re-twisted in the opposite
direction, without showing signs of fracture. It will be seen that
the wire is extremely strong and the moderate stress of from 35
to 50 tons per square inch, which at most it is called upon to with-'
stand in a gun, is far less than what it could endure with perfect'
safety.

The wire after being manufactured is made up into hanks for
storage purposes; but when required for gun construction it is
thoroughly cleaned and wound on a drum R about 3 ft. 6 in. in
diameter, which is placed in one portion of the machine in connexion,
with a powerful band friction brake M. The wire is then led to the
gun A placed between centres or on rollers B.B. parallel to the axis
of the wire drum. By rotating the gun the wire is drawn off from the
drum against the resistance of the band brake, which is so designed
that, by adjusting the weight S suspended from the brake strap,
any desired resistance can be given in order to produce the necessar>-
tension in the wire as it is being wound on the gun. The stress on




Fig. 20. — Wire-winding Machine.



HISTORY AND CONSTRUCTION]



ORDNANCE



197



the wire is indicated on a dial, and the headstock, containing the
drum of wire, is capable of being moved along the bed G by a
leading screw H, driven by a belt through variable speed cones I;
the belt is moved along the cones by forks J, traversed by screws K,
which in their turn are actuated by chain belts from the hand
wheel L. The traversing speed is regulated to suit the speed of
winding by moving the belt along the speed cones.

The wire is rectangular in section, 0-25 in. wide and o-o6 in. thick,
and after it has been wound on to the gun it presents a very even
surface which requires little further preparation. The diameter
over the wire is gauged and the jacket or other covering hoop is
carefully bored equal to this, if no shrinkage is to be allowed; or the
dimension is diminished in accordance with the amount of shrinkage
to be arranged for.

The gun is built up, after wiring, in the same manner as a gun
without wire, the jacket or other hoop being heated in the vertical
gas furnace and when hot enough dropped into place over the wire,
cooled by the ring of water jets at the end first required to grip and
kept hot at the other, exactly as before described.

The machine arranged for rifling modern guns is very similar
to that employed for the old muzzle-loaders; it is a special tool
Riniae "^^"^ '" 8"" construction only (fig. 21), and is in reality
operation ^ copying machine. A steel or cast-iron bar J which
forms the copy of the developed rifling curve is first
made. The copying bar — which is straight if the rifling is to be uni-
form but curved if it is to be increasing — is fixed, inclined at the



bullet, from the muzzle. In 1856 Russia made a large number of
experimenls with a rifled gun invented by Monligny, a Belgian;
this was not a success, but in England the guns invented by
Major Cavalli, in 1845, and by Baron Wahrcndorff in 1846,
obtained some measure of favour. Both these guns were breech-
loaders. The Cavalli gun had a bore of 6-5 in. diameter; it was
rifled in two grooves having a uniform twist of i in 25 calibres,
and the elongated projectile had two ribs cast with it to fit the
grooves, but no means were taken to prevent windage. The
Wahrendorff gun had an enlarged chamber and the bore of
6-37 in. diameter was rifled in 2 grooves; the projectile had ribs
similar to that for the CavaOi gun; but Wahrendorff had also
tried lead-coated projectiles, the coating being attached by
grooves undercut in the outside of the shell. In 1854 Lancaster
submitted his plan of rifling; in this (fig. 22) the bore was made
of an oval section which twisted round the axis of the gun from
the breech to the muzzle; a projectile having an oval section
was fired. Several old cast-iron guns bored on this system
burst in the Crimean War from the projectile wedging in the
gun. In 1855 Armstrong experimented with a breech-loading
rifled gun, firing a lead-coated projectile. The rifling consisted




Fig. 21. — Rifling Machine.



proper angle, to standards K on the machine. The cutting tool is
carried at one end C of a strong hollow cylindrical rifling bar B, the
other end of which is fixed to a saddle M. This is moved along the
bed of the machine by a long screw N, and the rifling bar is conse-
quently either pushed into the gun or withdrawn by the motion of
the saddle along the machine. During this motion it is made to
rotate slowly by being connected to the copying bar by suitable
gearing I. It will thus be seen that the cutting tool will cut a spiral
groove along the bore of the gun in strict conformity with the
copy. In most English machines the cutting tool cuts only as the
rifling bar is drawn out of the gun; during the reverse motion the
cutter F is withdrawn out of action by means of a wedge arrange-
ment actuated by a rod passing through the centre of the rifling bar,
which also pushes forward the cutter at the proper time for cutting.
One, two or more grooves may be cut at one time, the full depth
being attained by slowly feeding the tool after each stroke. After
each set of grooves is cut the rifling bar or the gun is rotated so as
to bring the cutters to a new position. In some foreign machines
the cut is taken as the rifling bar is pushed into the gun.

Rifling is the term given to the numerous shallow grooves
cut spirally along the bore of a gun; the rib between two
Riaiar. grooves is called the " land." Rifling has been known
for many years; it was supposed to increase the range,
and no doubt did so, owing to the fact that the bullet having
to be forced into the gun during the loading operation became
a mechanical fit and prevented to a great extent the loss of gas
by windage which occurred with ordinary weapons. Kotter
(1520) and Banner (1552), both of Nuremberg, are respectively
credited as being the first to rifle gun barrels; and there is at the
Rotunda, Woolwich, a muzzle-loading barrel dated 1547 rifled
with six fine grooves. At this early period, rifling was applied
only to small arms, usually for sporting purposes. The
disadvantage of having, during loading, to force a soft lead (or
lead-covered) ball down a bore of smaller diameter prevented
its general employment for mihtary use. In 1661 Prussia
experimented with a gun rifled in thirteen shaUow grooves, and
in i6q6 the elliptical bore — similar to the Lancaster — had been
tried in Germany. In 1745 Robins was experimenting with
rifled guns and elongated shot in England. During the Peninsular
War about 1809, the only regiment (the " Rifle Brigade,"
formerly called the 05th) equipped with rifled arms, found con-
siderable difficulty in loading them with the old spherical lead



of a large number of shallow grooves having a uniform twist
of I in 38 calibres. When the gun was fired the lead-coated
projectile, which was slightly larger in diameter than the bore
of the gun, was forced into the rifling and so gave rotation to
the elongated projectile. Whitworth in 1857 brought out his



WHITWORTH BORE



lAHCASTER OVAL BORE





EARLY ARHSTROHC CROOVI



s®i



k1



FRENCH GROOVE

For *Luddtd frojiCCil**




POLYOROOVE (//ooM 6eccion }



^m



MODERN GROOVE {.£ar,j T^pt)



%



I %



m



KRUPP GROOVE



.w^



MODERN GROOVE (/acese Typt)



%



' ^



Fig. 22. — Sections of Rifling.

hexagonal bore method of rifling and a projectile which was
a good mechanical fit to the bore. Good results were obtained,



198



ORDNANCE



[HISTORY AND CONSTRUCTION



but although this system had certain advantages it did not
fulfil all requirements.

In 1863, England re-opened the whole question, and after
exhaustive trials of various inventions decided on the adoption
of the muzzle-loading type foi all guns, with the French system
of rifling. This system was invented in 1842 by Colonel Treiiille
de Beaulieu and consisted of a few wide and deep grooves which
gave rotation to a studded projectile. At the first trials two
grooves only were tried, but the number was afterwards in-
creased to three or more, as it was found that two grooves only
would not correctly centre the projectile. The adoption of the
muzzle-loading system with studded shot was a distinctly
retrograde step, as a considerable amount of clearance was
necessary between the bore and projectile for the purposes of
loading, and this resulted in the barrel being seriously eroded
by the rush of gas over the shot, and also led to a considerable
loss of energy. In the Wahrendorff and Armstrong systems
however the lead-coated projectiles entirely prevented windage,
besides which the projectile was perfectly centred and a high
degree of accuracy was obtained.

Shunt rifling was a brief attempt to make loading by the
muzzle easy without forfeiting the centring principle: in this
the rifling varied in width and in depth, at different portions of
the bore in such a manner that, during loading, the studs on the
projectile could move freely in the bore. When the gun was fired
the studs of the projectile were forced to travel in the shallow
part of the rifling, thus gripping and centring the projectile as
it left the muzzle.

With uniform rifling on the French system, the few studs —
generally two per groove — had to bear so high a pressure to
produce rotation that they sometimes gave way. This subject
was investigated by Captain (Sir Andrew) Noble, who showed
that by making the rifling an increasing twist, commencing with
no twist and gradually increasing until the necessary pitch was
obtained, the maximum pressure due to rotation was much
reduced. Increasing rifling was consequently adopted, with
beneficial results.

In order to prevent the heavy erosion due to windage, a gas
check was adopted which was attached to the base end of the
studded projectiles. In some guns the number of grooves of the
rifling was sufficiently great to admit of rotation being insured
by means of the gas check alone; in these guns studded pro-
jectiles were not employed, but the gas check, called " auto-
matic," to distinguish it from that fitted to studded projectiles
was usually indented around its circumference to correspond
with the rifling of the gun. It was found that the studless
projectile had considerably greater range and accuracy than the
studded projectile, with the additional advantage that the shell
was not weakened by the stud holes.

The introduction of the plain copper driving band for rotating
projectiles with breech-loading guns included a return to the
polygroove system with shallow grooves; this still exists, but the
continuous demand for greater power has had the effect of in-
creasing the number of grooves from that at first considered
necessary, in order to keep the rotating pressure on the driving
band within practical hmits.

Many ingenious devices for giving rotation and preventing the
escape of gas past the projectile were tried in the early days of
modern rifling. Experiments of this nature stiU continue to be
made with a view to improving the shooting and to prevent the
erosion of the bore of the gun. Briefly considered, without
going into any detail of the numerous plans, all rotating devices
fitted to projectiles can be divided into three classes — the
"centring, " the " compressing " and the " expansion " systems.
The two last named almost invariably include the " centring "
type. Studded (fig. 23) and Whitworth (fig. 24) hexagonal
projectiles, which can freely slide in the bore, come under the
first system.

In the compression class the coating or rings on the projectile
are larger in diameter than the bore and when fired the coating
(or rings) is squeezed or engraved by the rifling to fit the bore —
the projectile is consequently also centred. The old-fashioned



lead-coated shell (fig. 25), and the modern system of plain copper
driving bands (fig. 26), come under this class. Most variety
exists in the expansion type, where the pressure of the powder
gas acts on the base of the projectile or on the driving ring and
compresses a lead, copper or asbestos ring into the rifling grooves.
One of the earhest was the Hotchkiss (1865) shell (fig. 27), in
which a separate base end B was driven forward by the gas
pressure and squeezed out the lead ring L into the rifling. The
automatic gas check (fig. 28), and the gas check driving band
(fig. 29), belong to this system; in the last the lip L is expanded
into the rifling groove. In fig. 30 a copper driving band is




Fig. 23.



Fig. 24.



Fig. 25.



£^ <^ .B^^



Fig. 26



Fig. 27.



Fig. 28.



->



Fig. 29. Fig. 30.

tiGS. 23-30. — Proiectilcs for Rifled Ordnance.

associated with an asbestos packing A, contained in a canvas
bag or copper casing made in the form of a ring on the principle
of the de Bange obturator; but the results of this have not been
entirely satisfactory.

It win be seen that with breech-loading guns the projectile
is better centred, and the copper driving band forms a definite
stop for the projectile; and, in consequence, the capacity of
the gun chamber is practically constant. In addition, the use
of a copper driving band ensures a uniform resistance while
this is being engraved and the projectile forced through the
gun, and also prevents the escape of gas. These elements
have a very great influence on the accuracy of the shooting, and
fully account for the vastly superior results obtained from breech-
loading ordnance when compared with the muzzle-loading type.
Driving bands of other materials such as cupro-nickel and
ferro-nickel have also been tried.

Many authorities beUeve that the best results are obtained
when the projectile is fitted with two bands, one near the head and
the other near the base, and no doubt it is better centred when
so arranged, but such shot can only be fired from guns rifled vrith
a uniform twist, and it must also not be forgotten that the groove
formed for the front band in the head of the projectile necessarily
weakens that part of the projectile which should be strongest.

Projectiles with a driving band at the base only can be fired
from guns rifled either uniformly or with increasing twist.

The introduction of cordite (q.v.) about 1890 again brought
into special prominence the question of rifling. The erosion
caused by this explosive soon obliterated the rifling for some 4
or 5 cahbres at the breech end. The driving band of the shell
consequently started with indifferent engraving, and with the
increasing twist, then in general use, it was feared that the wear
would quickly render the gun useless. To remedy this the late
Commander Younghusband, R.N., proposed straight rifling,
which was adopted in 1895, for that portion of the rifling mostly
affected by the erosion, with a gradual increase of the twist
thence to the required pitch at the muzzle. Thus, any erosion
of the straight part of the rifling would not affect that portion
giving rotation, and it was argued that the gun would remain
efficient for a longer period. The defect in this system is that
when the projectile arrives at the end of the straight rifling it
has a considerable forward velocity and no rotation. Rotation
is then imparted by the increasing twist of rifling, and the



HISTORY AND CONSTRUCTION]



ORDNANCE



199



resulliag pressure on the engraved ribs of the driving band rises
suddenly to a maximura which, in high velocity guns, the
driving band is unable to resist. For this reason the straight
portion at the commencement of the rilling has been discarded,
and with high power guns firing a slow burning propcllant uniform
rifling has again found favour.

It is evident that in order that a projectile may have a definite
amount of spin as it leaves the gun a determinate amount of work
must be imparted to rotate it during its passage along the rified
portion of the bore. Put briefly, this work is the sum of the products
of the pressure between the engraved ribs on the driving band and
the lands of the rifling in the gun multiplied by the length of the
rifling over which this pressure acts. Sir Andrew Noble has proved
theoretically and e.xperimentally (see Phil. Mag., 1863 and 1873;
also Proc. Roy. Soc. vol. 50) that the rotating pressure depends on
the propelling pressure of the powder gas on the base of the projectile
and on the curve of the rifling. If this curve was so proportioned
as to make the rotating pressure approximately constant along the
bore, the result was an increasing or progressive curve partaking
of the nature of a parabola, in which case it was usual to make the
last two or three calibres of rifling at the muzzle of uniform twist
for the purpose of steadying the projectile and aiding accuracy.

In uniform rifling the curve is a straight line and the rotating
pressure is consequently mainly proportional to the propelling gas
pressure. The pressure for rotation with uniform rifling therefore
rises to a maximum with the propelling pressure and falls as it
becomes less towards the muzzle.

With increasing rifling, owing to the angle of twist continually
changing as the projectile travels along the bore, the ribs originally
engraved by the rifling on the driving band are forced to change their
direction correspondingly, and this occurs by the front surface of
the ribs wearing away. They are therefore weakened considerably,
and it is found that with high velocities the engraved part of the
band often entirely disappears through this progressive action.

It will thus be seen that although an increasing twist of rifling
may be so arranged as to give uniform pressure, it is evident that
if wear takes place, the engraved rib becomes weaker to resist shearing
as the shot advances, and the rate of wear also increases owing to
the increase of heat by friction. With the very narrow driving
bands used for low velocity guns this action was not so detrimental.

With the longmodern guns and the high muzzle velocities required,
the propelling gas pressures along the bore rise comparatively slowly
to a maximum and gradually fall until the muzzle is reached. The
pressure of the gas at all points of the bore is now considerably higher
than with the older patterns of B.L. guns.

For modern conditions, in order to obtain an increasing curve
giving an approximately constant driving pressure between the
rifling and driving band, this pressure becomes comparatively high.
The maximum rotating pressure, with uniform rifling, is certainly
somewhat higher, but not to a ver>' great extent, and as it occurs
when the projectile is still moving slowly, the wear due to friction
will be correspondingly low; the pressure gradually falls until the
muzzle is reached, where it is much lower than with increasing
rifling. The projectile thus leaves the gun without any g/eat
disturbance from the rifling pressure. Further, as the band is
engraved once for all with the angle it will have all along the bore
the pressure is distributed equally over the driving face of the
engraved ribs instead of being concentrated at the front of the ribs
as in progressive or increasing rifling.

The following formulae showing the driving pressures for increas-
ing and uniform rifling are calculated from Sir Andrew Noble's for-
mula, which Sir G. Greenhill has obtained independently by another
method.

Let R =total pressure, in tons, between rifling and driving band.
G = gaseous pressure, in tons, on the base of the projectile.
r = radius, in feet, of the bore.
;uT = coefiicient of friction.
p = radius of gyration of projectile.
6 = angle between the normal to the driving surface of groove

and radius.
fe = the pitch of the rifling, in feet.
fe = cotangent of angle of rifling at any point of rifling.
M = weight of the projectile in pounds.
c = the length, in feet, travelled by the projectile.
Then for parabolic rifling



R =

For uniform rifling
R =



2p'{Gz + Uv'-)



(r'-fe'+4pV) sin 5 . 2ij.,kz(fr



r'}



2irp'G

ti,{2Tv p-k-rh) {2Trp''-\- rhk) sin 6



U + k^)i ' (fe^+sin^ay

For modern rifling 5 = 90°; therefore sin 6 = i ; by which the above
expressions may be considerably simplified.



For parabolic rifling

2p'(4o'+fe')}(Gz + Mt'^)

kr^(k-2^,,Z)+2p-z{2Z+lJL,ky

For uniform rifling we can write hk = 2Tir and the expression reduces

to

pHlJtk-V: ,0.



R=-



"^■(p^*-g



+P=+r-



I'ig. 31 shows graphically the calculatetl results obtained for a
4-7-in. 50-calibre gun which has a shot travel of 17-3 ft.; the pressure



;r

1



















T

1


/


^,








i.«^£?


^rCiffctMliMii


ATn^f^l I


/


\




,e/^i"4j^^^ "


''A'




i


/




Nil


-^












/ /




s


^












//






^V












//








^5%^..








/










^


p-.




/














"" - - .


. :,


/




































f


















a


4


6


e


.1


14 (


s le



FEET

4 7 INCH 50 CALIBRE GVI^
Fig. 31. — Pressure Curves (uniform and increasing twist).

curse A is for a rifling twist increasing from i in 60 calibres at the
breech to I in 30 calibres at the muzzle; curve B is for rifling having
a uniform twist of 1 in 30 calibres.

It must be remembered that this comparison is typical for modern
conditions; with old-fashioned guns firing black or brown powder
the maximum rotating pressure for uniform rifling could attain a
value 50 7o above that for increasing rifling.

In this example, with the increasing twist there is a loss of energy
of about 11% of the total muzzle energy, and for the uniform
rifling a loss of about 8%. This explains the reason for uniformly
rifled guns giving a higher muzzle velocity than those with increasing
rifling, supposing the guns to be otherwise similar.

The pitch of the rifling or the amount of twist to be given to it
depends altogether on the length of the projectile; if this is short
a small amount of twist only is necessary, if long a greater amount
of twist must be arranged for, in order to spin the shell more rapidly.
Sir G. Greenhill has shown that the pitch of the rifling necessary to
keep a projectile in steady motion is independent of the velocity,
of the calibre, or of the length of the gun, but depends principally
on the length of the shell and on its description, so that for similar
projectiles one pitch would do for all guns.

Table I., on following page, has been calculated from Greenhill's
formula.

In most modern guns the projectile varies in length from 3-5 to
4 calibres, so that the rifling is made to terminate at the muzzle
with a twist of I turn in 30 calibres, which is found ample to ensure
a steady flight to the projectile. In the United States a terminal
twist of I in 25 calibres is often adopted; Krupp also uses this in
some guns. With howitzers the projectile may be 4-5 calibres long,
and the rifling has to be made of a quicker twist to suit.

If the gun has, as is usually the case, a right-hand twist of rifling
the projectile drifts to the right; if it has a left-hand twist the
drift takes place to the left. The drift increases with
the range but in a greater ratio; further, the greater the
twist {i.e. the smaller the pitch of rifling) the greater the drift. On
the other hand the smooth B.L. projectiles drift less than studded
M.L. projectiles.

To find the angle, usually called the permanent angle of deflection,
at which the sights must be inclined to compensate for the drift,
a number of shots are fired at various ranges. The results obtained
are plotted on paper, and a straight line is then drawn from the point
representing the muzzle through the mean value of the plotted
curve.

The early guns were fired by inserting a red-hot wire into the
vent, or by filling the vent with powder and firing it by a red-
hot iron. Slow match held in a cleft stick afterwards
took the place of the hot iron, and this again was '^'""s
replaced by a port-fire. Filling the vent with loose meats.
powder was inconvenient and slow, and to improve
matters the powder was placed in a paper, tin or quill tube



Online LibraryHugh ChisholmThe Encyclopædia britannica; a dictionary of arts, sciences, literature and general information (Volume v. 20) → online text (page 72 of 353)