Page:Aircraft in Warfare (1916).djvu/131

Rh the volume of the bullet to receive the charge, and consequently, in view of the relatively low density of the explosive (about 1.6 in the case in point), the weight of the burster cannot be more than some 2 or 3 per cent, of the total. Taking the figure for cordite as representing the energy of the burster explosive, this means, in the case of the Service rifle, about 5 or 8 grains, or 1,300 ft.-lb, energy. But the efficiency of the burster is not likely to be higher than that which we associate with the main charge—it is at some advantage, inasmuch as there is no confined barrel to the walls of which heat is lost, but it is at a serious disadvantage, in that the explosion is not with any certainty confined to its work. It is doubtful whether of the 1,300 ft.-lb, total more than 300 ft.-lb, on an average will be usefully expended. We are thus led to appreciate the attributes of the explosive bullet, and more generally the explosive shell, in true perspective. The explosive only adds to an initial energy content of 2,000nbft.-lb, as due to velocity, a matter of about 300 ft.-lb, in available explosive energy, a quantity representing an addition of only 15nbper cent. It is at once evident that the value of the explosive charge is less due to its direct action than to the fact that by its spreading or scattering effect on the projectile the kinetic energy is used to better advantage. In other words, the explosion is effective as a means of initiating or causing the expansion of the bullet rather than as acting directly by its own destructive power. In the case of large shells the proportion of burster charge to total weight can be increased, and so the direct effect is relatively more important; for armour-piercing projectiles, however, the proportion is no higher than in the example taken—i.e., about 3 per cent. It might be imagined that the employment of some higher explosive would give a capacity of greater direct bursting energy, but the high