AMMUNITION - TECHNICAL A round of small arm ammunition, commonly called a cart ridge, consists of (a) a cartridge case, (b) percussion cap, (c) propellent charge and (d) a bullet. For all S.A.A. certain stand ards of accuracy and range are necessary, and erosion, wear, metallic fouling, and hang fires should be eliminated.
The cartridge case is made of solid drawn brass and is shaped to suit the chamber of the weapon. The front of the case is soft, to allow for the necessary expan sion for gas sealing purposes, whereas the rear end is hard to give the necessary strength for extraction. A flange or groove is provided at the base to facilitate the extraction of the empty case. A small chamber is formed at the base to house the cap, and fire holes are provided for the ignition flash.
(b) The percussion cap is made of brass or copper and fits accurately into the recess in th,, base of the cartridge case. It is secured by pressing over the metal of the case. The cap is filled with suitable composition which is readily fired by percussion. Owing to a tendency to deterioration of the composition under warm and damp conditions, the modern practice is to overload the cap and protect it by varnishing or other means.
(c) The propellent charge may be either nitro-cellulose powder, which is the custom in the United States of America, or one con taining a proportion of nitro-glycerine as in British cordite. It is claimed for nitro-cellulose that it gives the same velocities with lower maximum pressures, but it is more susceptible to dampness.
(d) A good bullet should be symmetrical in shape and mass. The modern rifle bullet consists of an envelope and core, the envelope being made of a fairly soft alloy and the core of lead. Cupro-nickel and soft steel have been used for envelopes gen erally, but in America an alloy of 90% copper has been tried with success. The shape of the rifle bullet is important in obtain ing a long range and the necessary accuracy. For this reason modern rifle bullets are provided with sharp points struck with circles of radius equal to 8 times the calibre. Stream-lining or boat-tailing the bases of rifle bullets will also give increased range ; but this practice has not been universally adopted, owing, probably, to difficulties of manufacture and possible inaccuracy of shooting. Machine-gun ammunition is similar to rifle ammuni tion and is ordinarily interchangeable.
A tracer bullet was introduced during the World War, for rifles and machine-guns. The base was stemmed with a burning composition, which was ignited by the propellent gases, and hence the bullet left a visible wake of smoke or flame. Armour piercing bullets have also been introduced to attack armoured cars, aircraft and similar targets which defeat the normal service bullet. They are jacketed with harder envelopes and have a core of specially treated steel, the space between the core and envelope being filled with a lead surround. These bullets can be fired from an ordinary service rifle and will penetrate about 0•25in. of armour. A further modification of this bullet of o. 5in. calibre can be fired from specially constructed weapons and will penetrate nearly i.00in. of armour.
In the British army the o.455in. calibre revolver, with its heavy, unjacketed lead-antimony bullet, has remained unchanged for 3o years. As a man-stopping pro jectile at point blank range it remains unbeaten, but its weight and poor accuracy at longer ranges limit its value. Most nations have adopted automatic pistols for their subsidiary weapon, and for these, jacketed bullets, either of copper or cupro-nickel, are employed. The various nations differ as to optimum calibre for pistol ammunition, but the tendency appears to be away from the light comparatively high-velocity bullet, such as the German 0.300 Mauser, which was sighted up to i,000yd., thus holding the pistol to its true role, namely, that of a man-stopping weapon at short range.
Theaeroplane bomb was developed in the World War and became an important offensive weapon. The main difference between aeroplane bombs and gun projectiles is one of strength. The latter may have to attain a muzzle velocity of about 2,000ft. per sec. in the length of the piece, and this entails pressures running up to 20 tons to the square inch. The former is merely dropped, so that the stresses on it when falling are very little greater than those encountered in normal handling and transport, and it is only when penetration of concrete build ings or armoured decks is sought that anything more than a thin steel case is required to contain the H.E. filling. As regards shape, the terminal velocity of an aeroplane bomb is never above ',Too f t. per sec., hence the stream-lining of the tail is just as im portant as the contouring of the head. Most bombs are therefore pear-shaped, with vanes attached to the cone of the tail to ensure that the bomb drops nose first.
Toinitiate the detonation of the H.E. filling on impact with the target, fuses or similar devices are used. These are usually simple mechanisms depending for their arming on the unscrewing of vanes by the air stream whilst falling. In general a safety pin, which is only withdrawn from the fuse when the airman drops the bomb, is used as an additional safety precaution. The building up of the detonation wave is accomplished by a central exploder, which may run the whole length of the bomb or, as in gun shell, only a few inches into the H.E. filling. (C. W. F.)
