Page:Aircraft in Warfare (1916).djvu/133

Rh bullet is so to proportion things that under the average conditions the degree of expansion is that found to be most desirable; thus the depth of the hole, or the extent of the slits, or the amount of the sheath cut away may be varied to whatever extent desired. The object to be attained is that the bullet shall expend its whole energy in inflicting the maximum possible injury, but at the same time it must not go to pieces or spread to such an extent that its penetration is lacking. In stopping big game it is necessary, not only that the energy should be wholly utilised, but also that it should be expended, as far as possible, in injury to the deep-seated vital organs. More recently Messrs. Westley Richards have brought out a modified form of expanding bullet in which the sheath is kept intact, but is not wholly filled by the lead core, there being an air-space in the fore end; this type (already illustrated in Fig. 13), expands to a moderate degree only, and retains a considerable power of penetration.

§ 62. Expansion due to Centrifugal Force. One of the main factors contributing to the spreading or expansion of a bullet is the centrifugal force of the bullet itself; all that is required of the impact is so to break down the structure of the bullet as to permit it to expand. The direction of motion of the peripheral portions of the bullet make at all points an angle with the axis of flight at least equal to the angle of the rifling, which is commonly about 1 in 10 to 1 in 12. This is the state of things when the bullet is discharged, but the actual angle rapidly becomes greater owing to the reduction of velocity, the speed of rotation being comparatively little affected. Thus at 1,000 yards range the velocity is reduced by half, and the relative direction of the skin of the bullet becomes about 1 in 6 to the line of flight. If then by a sudden impact or other means the bullet be