supports the weight of the bullets and prevents the bullets set- ting back on the shock of firing and crushing in the tin cup. and possibly exploding the gunpowder. In some cases the central tube is filled with gunpowder pellets, which by burning, increase the cone of dispersion of the bullets and give more smoke, which is exceedingly important for the observation of bursts in air. The interior of the shell is fitted with bullets set in resin, which, besides holding the bullets firmly, is ignited by the opening charge and so increases the smoke effect. The interiors of some shells are lined with brown paper in order to prevent the resin from adhering too firmly to the body of the shell.
The mouth of the shell is closed by a metal socket threaded for the reception of a fuze; the top end of the central tube is soldered to this fuze socket. When the gunpowder charge in the shell is exploded by a flash from the fuze down the central tube, the bul- lets are projected from the case to travel forward along the line of flight within a cone of small apex angle. The bodies of shrapnel are not intended to break up when the opening charge is exploded, but merely to act as containers to convey the bullets to the point of burst.
Another type of elongated shrapnel shell was formerly in use in which the burster was contained in the head. In this the head was firmly and the base very lightly attached to the body, so that on the explosion of the opening charge, the head and body remaining together were drawn over the bullets, and falling to the ground allowed the bullets to proceed on their course and scatter. In this pattern more bullets could be packed into a shell, owing to the elimination of the diaphragm and central tube; but instead of the closely grouped forward shower of bullets produced by the base burster, there was an open scattering of bullets, due to the check- ing, negative, effect of the opening charge on the bullets.
Normally field guns fire both high-explosive and shrapnel shell. Many attempts have been made to provide a " universal shell " which would combine the functions of both types. If the bullets of a shrapnel shell be packed in some high explosive instead of resin, then, on the time fuze igniting the base opening charge, the shell would open in the ordinary way, the high explosive (which as has already been shown is difficult to deto- nate) merely burning and giving useful smoke. But if a gaine, ig- nited only by the percussion portion of the fuze, be provided to act on some high explosive in the head of the fuze, then the whole of the high explosive, detonating on impact, would probably pro- duce sufficient disruptive violence to shatter the whole of the shell and destroy material.
The Germans in the World War employed a type of universal shell having a high-explosive filling in the head, with the fuze so arranged that when the shell is required to burst in air, the head of the shell is blown off bodily, flies forward with the bullets, and itself bursts when striking the ground. If, on the other hand the whole shell is burst on impact, the disruptive effect of the high explosive in which the bullets are packed ' breaks up the shell.
The Austrian universal shell is somewhat similar. These shell can be used in four ways, as a percussion H.E. without or with delay action, as a time shrapnel, and as a time H.E. The fuze is designed accordingly.
With the universal shell, there is a distinct loss of bullet capacity, with a consequent loss of shrapnel efficiency. It is therefore con- sidered, in some services, more practical and effective to carry two types of shell, high-explosive and shrapnel, and use them accord- ing to tactical requirements, than to attempt the complications in design and manufacture, mistakes and possibly failures in the field, entailed by the use of a type of universal projectile. 2
(c) Armour-piercing projectiles for maximum penetration, should be tempered so as to break rather than set up sensibly, and the stresses in the way of perforation and of fracture should be clearly distinguished. The main question is that of the striking energy modified by the projectile's power of holding together, which depends directly on the tenacity of the metal; and the capacity for taking a bursting charge would be of less importance than the strength of the head and walls. It appears probable, however, that the ultimate tenacity, as well as the limit of elasticity, would be the measure of the projectile's power. In direct impact, on deformation commencing, all penetration comes quickly to an end; but after commencing an injury, any
1 This packing of the shrapnel bullets in H.E. is not an in- separable element of the design. In some universal shell, the ordi- nary resin or other non-explosive material is used. (C. F. A.)
2 According to Schwarte (MUitiirische Lehren des Grossen Krieges) the German pattern of universal shell proved very disappointing in war; on the other hand the Austrian and other " Orisanz-Schrap- nell " shell based on Ehrhardt design were most successful.
(C. F. A.)
following up of the blow at the exact spot acts in so forcible a way that between the limit of elasticity and that of ultimate tenacity, a sensible amount of work must exist. Generally with projectiles for attack of soft armour, hardness is a necessity, and for attack of hard armour, tenacity is a necessity.
Armour-piercing projectiles may be divided into two classes. First come armour-piercing shell (fig. 7). in which the bursting charge is comparatively small, the head and point extremely hard, and the body softer to give greater tenacity. The success of the old Palliser projectiles depended upon the metal used, the mode of casting, and the form of the projectile and distribution of the metal. With regard to these points specially selected iron was used ; the projectiles were cast head down (to ensure density and sound- ness) in an iron chill with the result that the molten metal rapidly solidified and the qualities given to the head by white iron were intense hardness and crushing strength, but considerable brittle- ness; the form of the head was a fairly long elongated point, and the object in manufacture was to get the metal as far forward as possible so as to impress its momentum on the armour with- out acting through the medium of the walls of the shell, though the latter were necessarily thick; this method of manufacture obviously diminished the interior capacity and consequently the bursting charge of the shell.
As processes for hardening armour came to be introduced and used, the material for armour-piercing shell was necessarily changed to steel.
FIG. 7.
Owing to the liability to split spontaneously, due to the strains set up during the hardening process, the shell are stored for several months before being filled, and the bursting charge is contained in a thin aluminium container. The base is removable and a base adapter is fitted, the base being further secured by a copper gas- check plate, steel plate cover, and steel locking ring screwed to the adapter.
Base r-uze
Cap
Adapter
""^Primers Explosive
Bras* or Copper Container
Driving Band
FIG. 8.
Secondly, there are semi-armour-piercing shell (fig. 8), which are practically common shell pointed, designed to effect a certain amount of penetration of light armour 1 , and to contain a large burst- ing charge. The points are specially hardened, in some cases capped (as in fig. 9) and the bursting charge is held in a metal container.
FIG. 9.
Hard-faced armour defeats a projectile simply by fracture of the point and such fracture can in a great measure be prevented by a cap which protects the point when it meets the hard skin of the armour, whether the cap be hard and shattered or soft and crushed.
The first introduction of a cap was to allow a projectile to bite armour obliquely; but it is the value of a cap as a support to the point of the shell that has determined its use. Formerly the shapes of caps were designed without any consideration of the contour of
