Page:Aircraft in Warfare (1916).djvu/128



§ 58. ''Gun-Fire. The Energy Account.'' The kinetic energy of a projectile commonly represents from 10 to 30 per cent, of the total energy of the explosive or powder charge by which it is projected; the lower figure corresponds to the performance of a small-bore low-velocity rifle such as a rook rifle, the latter being that approached under the most favourable conditions by the military or big-game rifle. The British Service rifle with Mark VI, ammunition thus has an efficiency of approximately 28 per cent.; in the ordinary sportsman's "12-bore" the figure is about 11 per cent.

The total energy released on combustion by black powder is the equivalent in round numbers of 500 foot-tons per pound. The corresponding figure in the case of cordite is half as much again, approximately 750 foot-tons per pound; in general it may be taken that most of the explosives in common use have an energy content between 500 and 1,000 foot-tons per pound. In the case of the Service rifle with Mark VI, ammunition the weight of the powder (cordite) is 30nbgrains (0.0043 lb.), and the bullet 215 grains (0.0307 lb.), the velocity being 2,050 ft, per second. Thus the total energy of the charge is 0.0043 × 750 = 3.2 foot-tons, and the muzzle (kinetic) energy is 2,000 foot-pounds = 0.895 foot-ton; the efficiency, therefore, is 0.895/3.2 = 0.28, as already given. It is worthy of remark, en passant, that there is