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Rh pine, representing 3½ cubic inches of wood displaced. Taking this as a criterion, it is clear that if we can obtain the necessary rapidity of expansion, there is ample energy in a single hit to sever any ordinary wing or similar structural member.

§ 63. The Light Weight Shell. Apart from the question of the explosive or expansible bullet, we have already seen that the 14 oz. limit of projectile weight is an irksome restriction when we are dealing with aeroplane armament. Not only is the gun required weighty and cumbersome, but the weight of the ammunition is, save for machines of exceptional size, almost prohibitive. If we are able to adopt a weight of 6 oz. or 8 oz. in place of 14 oz., it will be possible to use a gun direct-mounted without the elaboration of recoil mechanism, and weighing from 40 lb. to 45 lb. In addition to this, the cartridges would weigh less than 1 lb. apiece, and provision could be made for some 300 rounds in a machine of present-day dimensions. For attack on other aeroplanes, such a shell would be almost as effective as one of twice the weight, and, owing to the recoil limit, the rate of fire can be doubled if the lighter shell be adopted.

It is convenient to make a distinction between the explosive bullet and the shell, even if the definition be considered somewhat artificial. The former is defined as containing a single charge, impact fuse and "burster" in one; the latter (the shell) contains, as well as the burster charge, an independent cap or detonator, and a fuse or mechanism, time or impact, for determining the instant of explosion. Many writers refer to the explosive bullet equally as a shell.

It is unnecessary to discuss the probability or possibility of the abandonment of the restriction imposed by the Declaration of St. Petersburg. We know that the clause in question was framed from humanitarian