"Metallic fouling" in the barrel is an other and ever-present trouble. It is produced by the bullet envelopes, usually composed of an alloy of copper and nickel, which, when travelling at a high velocity, are prone to leave behind small particles of the envelope adhering to the bore, thus spoiling its true cylindrical form and so causing inaccuracy in the shooting. Metallic fouling when steel envelopes are used, is practically negligible, but a difficulty with these which has not as yet been generally overcome is to manufacture a steel or other substance which, while being tough enough not to leave particles in the bore or to erode it unduly, will yet be soft enough to per mit of its expanding sufficiently to "bottom" in the grooves of the rifling, and so prevent escape of gas past the bullet and avoid the troubles that arise from such a cause. This expansion of the base of the bullet is known as "set up." In the United States metallic fouling has now been practically eliminated by the substitution of a jacket metal composed of copper 90 parts, zinc Io parts, for the usual cupro-nickel jacket.
A bullet of stream-line contour has of recent years come into prominence, and is employed by Switzer land and in the United States. Its great merit is that, owing to its shape, it far outranges the bullet having a cylindrical body and tail. Owing however to its tapering tail, which precludes the possibility of "set up," the difficulty of sealing the grooves against the gas pressure developed has not as yet been so generally over come, that such bullets, made in mass production, will continue to shoot accurately as the barrels suffer wear.
Armoured vehicles are no doubt still in the early stages of development, and the means to counteract them is yet to seek. It seems unlikely that reliance can be placed in the machine gun of the usual bore for this purpose, and that other or heavier weapons, possibly of an automatic nature, will be developed which will be able more adequately to deal with such vehicles. Allied to this problem is that of increasing the penetrative power of armour-piercing bullets. For penetration, a hard projectile having a high velocity is essential, but a diffi culty still to be overcome is the tendency of the very hard bullet to splinter without penetrating.
Capacity to vary the rate of automatic fire has much to recom mend it and should be capable of accomplishment. Until now, the only machine gun in which such a regulator is embodied is the French St. Etienne (Puteaux), since superseded by the Hotchkiss.
Text Book of Small Arms 59o9 (historical and technical on rifles and pistols). Official publication. E. W. Lloyd and A, G. Hadcock, Artillery. Its progress and present position. Historical and technical on early machine guns and artillery. Longstaff and At teridge, The Book of the Machine Gun
Historical, technical and general tactics. Maj.-gen. Reid, The Rev. Alexander Forsyth. T. F. Freemantle, The Book of the Rifle (19o1, historical and technical). Handbook of the Vickers Gun (official publication, 1923). Handbook of the Lewis Gun (official publication, 1918). Whelen, The American Rifle, 1918. (H. R. A.)