Projectiles

PROJECTILES Types of Projectiles.—Projectiles for ordnance may be di vided into two main classes, shot and shell. The only shot now found in modern armaments are proof shot, practice shot, paper shot and case shot. Proof shot are solid shot used for proving ordnance and charges. Practice shot are solid shot used for practice purposes. Paper shot are used to test gun mountings which cannot fire service projectiles in peace time, owing to their siting. They are made mainly of paper or pulp and their weight is calculated to exert the same stress on the mounting as a service round, but they break up in the bore when fired. Case shot generally consist of three or more long steel segments held in position inside a thin, tinned canister, the whole being filled with bullets. The top and bottom are formed of steel plates and in larger natures, the shot is stiffened by a central bolt. It is not much used in modern equipments.

The natures of shell now used are : common pointed or C.P. shell ; high explosive or H.E. shell ; shrapnel shell ; armour-pierc ing or A.P. shell; and special shell, of kinds such as smoke, star (illuminating) and incendiary. These various types of are employed because different effects are desired on the target, but there are certain properties common to all shell. For example, they must not break up in the gun when it is fired; they should give long ranges and accurate shooting and they should be cheap and easy to manufacture. It can, therefore, be seen that the design of a shell is a compromise between conflicting qualities, but as a result of experience the following facts are generally true.

Weight.

Roughly, the weight, in pounds, of a shell suitable for a given gun is half the cube of the calibre in inches. Length.—A shell should be at least 2 calibres but normally does not exceed 41 calibres in length. If a ballistic cap or hollow point is fitted the maximum length may be increased.

Shape.

The modern shell consists usu ally of a cylindrical body with a tapering head. An ogival head is generally con sidered the best shape for overcoming air resistance and ensuring accuracy but coni cal and other smooth shapes may be em ployed. Theoretically, with high velocity shell, the longer the head the greater is the range obtained, but in practice the length of head is limited by considerations of accuracy. With low velocity projectiles an increase of range may be obtained by stream lining or boat tailing the base, but the use of this device is restricted by prac tical considerations.

Material.

Modern shell are ordinarily all made of cast or forged steel.

Driving Bands.

To obtain rotation, a copper or alloy band is pressed into an undercut groove near the base of the shell. This centres the projectile and in conjunction with the rifling of the gun, gives the necessary rotation. With heavy shell two or three bands may be employed.

Caps.

To increase the penetration of pointed projectiles used against armour, solid caps of steel may be fitted over the points and fixed by soldering and in denting. These caps are employed with C.P. and A.P. shell.

c.p. Shell.

These shell are intended for the attack of light armour. They are prepared to take a base fuse and are filled with gunpowder or high explo sive. Sometimes the points may be specially hardened and fitted with caps to give better penetra tion. (See fig. I.) h.e. Shell.—High explosive, as a filling for artillery shell, was first suggested by Turpin in 1886, who advocated the use of picric acid in a dense form. With slight modifications, it was adopted by the French as melinite, by the Germans as granatf ullung 88, by the British as lyddite, and by the Japanese as shimose. Modern British H.E. shell are normally of forged steel with solid bases, a special steel base plate being fitted in a recess in the base to give added strength. The walls may be comparatively thin, which gives good effect against material, or, alternatively, the walls may be thick enough to give good effect against personnel. The nose of the shell is prepared to take a fuse. In some countries solid bases are not considered essential in these shell. Explosives used as H.E. shell fillings are ordinarily picric acid, TNT (tri nitro-toluene), and amatol, which is a mixture of TNT and am monium nitrate. Other substances used are dinitro-benzene trini troanisol and guncotton, and, during the World War, many .other fillings were tried. These explosives are generally inert and not easily detonated, and hence an exploder system is ordi narily found between the fuse and the filling itself. In same cases, where detonation gives little or no smoke, some smoke producing mixture is included in filled shell to assist observation of fire. A typical modern British H.E. shell is illustrated in fig. 2. The steel body is stout, giving good fragmentation. The filling is amatol, with a proportion of TNT to facilitate detonation. The exploder system in this particular case is represented by a game and an exploder. Fig. 3 illustrates a modern German H.E. shell evolved during the war. The filling calls for little comment. There are several points of interest in comparison with earlier shell. The base is closed by an adapter, which is contrary to British practice. Three driving bands are employed and a decoppering ring is fitted. Two fuse holes are provided, which permit of either nose or base fusing, or even the use of two fuses at the same time. This shell also pro vides a good example of the bal listic cap or false ogive.

Shrapnel Shell.

The shrap nel shell was invented in '784 by Lieut. Henry Shrapnel, R.A., and was originally called the "spheri cal case shot." The idea of the inventor was to keep the burst ing or opening charge as small as possible so that the velocity of the shell would be imparted to the bullets. After considerable delay this projectile was adopted by the British Government, and was apparently first used in ac tion against the French, at the battle of Rolica in i8o8. In 1852 the British army adopted the name "shrapnel" in honour of its inventor. With the development of ordnance the design of this shell has been modified, but the principle involved remains the same. The body of a modern shrapnel shell is made with thin walls, and it is closed either by a fuse socket or by a separate head, the part in either case being merely lightly attached. A fuse is screwed into the socket or head. The other parts of the shell are shown in the illustration. The bullets are made of heavy metal, but their weights vary with the size of shell. (See fig. 4.) The central tube may or may not be provided with powder pellets. The action of the shell is simple. When the fuse func tions a flash passes down the centre tube and ignites the opening charge, which pushes out the bullets and head.

A.P. Shell.

These shell are intended to penetrate armour and then burst effectively. The solid head is especially hardened and the walls are tough. They are generally fitted with caps to give an increased penetration. Old pattern shell may be filled with powder, but modern projectiles (fig. 5) are filled with H.E. Special Shell.—Gas shell were introduced by the Germans during the World War, and were developed by them into weapons of great offensive power. Ordinarily shell bodies of H.E. design were utilized and filled with a liquid or solid substance which volatilized on exposure to the air, giving a concentration of gas sufficiently strong to disable an unprotected man. The shell were usually opened by a small charge of explosive, the fuse employed being of the instantaneous type. In later patterns of shell the chemical ingredients were inclosed in a bottle which was buried in an ordinary H.E. filling. The shell functioned as an ordinary H.E. shell with the additional deleterious effect due to the chemi cal.

Smoke shell are really another product of the World War. In design they resemble gas shell and are filled with composition intended to give smoke clouds for purposes of concealment.

They are actuated by direct action fuses and contain small H.E.

opening charges. Incendiary shell, also introduced by the Ger mans, contain incendiary substances and are used with either time or percussion fuses. They call for no further comment. The star shell has many advantages. The latest type of illuminating shell may be considered as well represented by that illustrated in fig. 6. There is a time fuse which can be set for any time up to 33 seconds. When the fuse func tions the flash from the maga zine ignites the powder in the dome of the shell and blows off the head of the shell. The flash from the powder passes down a side channel to the powder charge in a small magazine in the base of the shell ; the powder explodes and ejects the star and parachute from the body, and at the same time the star composition in its case is ignited by means of quick match strands and powder pellets embedded in the composition. After ejection, the parachute opens and keeps the star floating in mid-air until it burns out.

Cartridges.

Cartridges for ordnance are divided into two main classes, called breechloading or B.L. and quickfiring or Q.F., and each class is subdivided into gun and howitzer cartridges.

The terms B.L. and Q.F. are essentially British, but in other countries the two classes are distinguished by different names.

Propellents.

The actual propelling charges are smokeless propellents of the nitrocellulose type, with or without an ad mixture of nitroglycerine. They are somewhat difficult to ignite, and hence an igniter of gunpowder is usually embodied in the cartridge. The propellent may be manufactured in various forms, e.g., sticks or cords, tubes, flakes, and disks, the form and size providing a means of controlling the burning. Well known mod ern propellents of various forms are Cordite, Rohrenpulver, N.C.T., Ballistite, Ringpulver and Flake.

b.l. Cartridges.

B.L. cartridges for guns consist of cylindri cal bundles of propellent enclosed in silk bags with shalloon disks accidental ignition. On the other hand, brass is expensive in itself and adds to the weight of the cartridge, entailing increase in trans port. Unsuccessful attempts have been made to introduce other metals, such as steel or aluminium. (See fig. 8.) Means of Ignition.—B.L. cartridges are ignited by means of tubes. A tube in its simplest form is a brass cylinder containing a charge of fine grain powder, which is ignited by friction, by percussion (fig. 9) or electrically. The tube is a separate part of the round in this case, is inserted in the vent of the gun and fired by the breech mechanism. Q.F. cartridges carry their own means of ignition, which are usually called primers or caps. A typical modern percussion primer is il lustrated in fig. 1 o. The cap of the primer is fired by the impact of the firing mechanism, and the subsequent flash ignites the pow der in the magazine and thence the propellent charge.

Fuses.—A fuse is a piece of mechanism which is employed to initiate the bursting, explosion, or detonation of a shell at the re quired place or time. Embodied in the fuse design are devices which make it safe in handling, transport, and during the pas sage of a shell up the bore of a gun.

Fuses may be classified as follows: (1) Percussion fuses (a) Direct action (D.A.), (b) Graze action, nose or base. (2) Time, or time and percussion fuses, combined (a) Combustion, (b) Mechanical or clockwork. (I) (a) Direct action fuses function as a result of a direct blow on the nose, a hammer or needle being forced on to a tonator. A modern pattern of D.A. fuse is the British fuse No. io6 illustrated in fig. II, from which its general construction will he understood. It is protected before loading by a safety cap, which is removed by hand. A split steel collar is interposed between the underside of the hammer head and the top face of the fuse body, and round this collar the safety tape is wound. On firing, the tape weight is gripped between the hammer head and body. When the shell leaves the bore the weight is released, flies off, unwinds, and carries the tape with it, tearing away the containing gunpowder stitched on to one or both ends. With heavy charges, the cartridge may be made up in part-charges and loops provided for lifting. For howitzers, the cartridges are made up in portions which allow varying charges to be used, and consist of a mushroom shaped core with rings or bundles of pro pellent attached by tape. (See fig. 7.) Q.F. Cartridges.—The essential feature of these cartridges is the brass case which carries the propellent. With small guns the cartridge case is usually attached to the shell, but in heavier calibres the cartridge is a separate component. The use of the brass case in certain circumstances leads to rapidity of fire and simplification of breech mechanisms and it gives safety against split collar. The hammer is then supported only by a thin shear ing wire. On impact, the hammer is driven in, shearing the copper wire, the detonator is fired, and in turn fires the maga zine. A safety shutter is provided, which only opens after the shell leaves the bore of the gun. Another type of D.A. ;use, somewhat less sensitive than the ordinary type, is the direct action impact type (D.A.I.). Such fuses merely differ from ordinary D.A. type in that the suspension of the needle or hammer is very much stronger, and hence the fuse requires a stronger blow on the nose in order to make it function.

(b) Graze fuses or check action fuses function as a result of the forward movement of a graze pellet relatively to the main body of the fuse. When the shell receives a check in velocity a pellet carrying a detonator moves forward on to a fixed needle or alternatively a needle pellet moves on to a detonator. A typi cal nose graze fuse is illustrated in fig. 12. The illustration repre sents the German fuse Kz. f. Spgr. m. K., and shows its general construction. Before firing, the detonator pellet is kept away from the needle by five interlock ing brass leaves held in position by a brass ferrule supported on a split brass sleeve. On firing, the ferrule sets back clear of the safety leaves and rebound is pre vented by two lugs on the sleeve. When the shell leaves the bore, the brass leaves open out one by one under the influence of cen trifugal force, leaving the fuse in a sensitive condition or "armed." Creep action of the detonator pellet during flight is prevented by the so-called creep spring. On graze, the pellet flies forward on to the needle and the detonator fires, the flash passing through a hole in the pellet to the exploder in the shell. A practice common in German design is to arrange a combination of direct and graze action effects in one fuze. In this type the detonator is housed in a movable pellet which functions in the usual way. The needle is formed on the inner end of a rod, the outer end of which projects from the top of the fuse. On im pact, the detonator pellet moves forward on to the needle as in an ordinary graze fuse, but in addi tion to this action the needle is also forced on to the detonator by direct action.

(2) A time fuse is one which can be set to burst a shell at a certain predetermined time after firing. A time and percussion fuse, commonly known as a T and P fuse, embodies, in addition to the time mechanism, a graze percussion mechanism which will function independently should the shell strike any object in flight or on impact with a target. Time fuses are divided into two main classes, (a) burning or composition and (b) mechanical or clockwork. The modern composition fuse is exemplified by the British T and P No. So. In this fuse the time is measured by the burning of a train of black powder which is compressed into annular grooves in adjustable rings. The firing of the gun initiates the burning of the rings and eventually the flash reaches the magazine and thence the opening charge of the shell. The movable ring type of time fuse is almost universal but a notable exception may be noted in French fuses of type No. 23-31, which is set by punching a hole at the appropriate point in a composition filled lead tube by a machine called a debouchoir. (See fig. 13.) The use of burning composition in time fuses is by no means ideal, and for many years experiments have been carried out with a view to obtaining a clockwork or mechanical apparatus. Vari ous patterns were tried but none was satisfactory until 1916, when the Germans brought into use a clockwork fuse Doppel ziinder 16 (T and P fuse 1916 pattern) which may be considered as typical of this class. This fuse is illustrated in figs. 14 and 15, the illustrations being diagrammatic and the description which fol lows is of principle and arrangements only. The clock train is driven, as in a watch, by a coiled spring in a barrel, but the escapement is original and peculiar. A straight steel spring take: the place of the hair-spring, which would be rendered useless by the effect of rotation and shock of discharge, and as tile length of the straight spring is adjustable, the movement of the pallet, of the balance, and therefore that of the escapement wheel and the clock train, is controlled and regulated. A horizontal hand, the position of which depends on the setting of the fuse, has, on its under surface, a notch, into which fits the upturned end of the lever at the top of the striker. When the clock train is started the hand moves round with it, but is prevented from rising and releasing the lever by a ring attached to the conical housing of the fuse. This ring is provided with two slots into which the hand can fit ; thus, when the clock is working, the rotation brings the hand into coincidence with the slots, and when forced up by the action of a small spring it releases the upturned end of the lever. The striker, previous to firing, has been held in the safe position by a collar on it, which rests on a shoulder of the centrif ugal bolt, but when this bolt is moved away by the rotation of the shell the outer end of this shoulder still rests on a steel pin. When the upturned end of the lever is freed from the notch in the lower side of the hand, as previously described, it flies out and rotates the striker, so that the collar clears the steel pin and allows the striker to fall and fire the detonator. The setting of the fuse and the hand is accomplished by turning the housing with a suitable key, this housing being free to move before firing. On discharge it is very ingeniously clamped to the body of the fuse by means of steel pins in a ring in its under surface. This ring sets back and the pins are driven through the flange of the clock case, a groove being turned on its under side to thin the metal and thus to allow of easy penetration. The clock train, wound up like a watch, is started at the moment of firing by the setting back of a detent.