ARTILLERY AMMUNITION Types of Projectiles.—Twogeneral types of projectiles are used for field, siege and coast artillery known as shell and shrapnel. Shell are made of steel and are filled with low explosives (black powder), high explosives (TNT) or chemicals. Low ex plosive shell produce fragments upon explosion ; high explosive shell, blast effect and fragments; and chemical shell, gas or smoke cloud effect. Other types such as star or illuminating shell are used for special purposes. Artillery shell are made in sizes from slightly over one inch in diameter, weighing about one pound to i6 inches in diameter, weighing over a ton. Shrapnel are filled with a number of balls and when the time fuse, with\ which a shrapnel is fitted, functions, the powder charge of the shrapnel is exploded. The balls are expelled forward in the form of a cone, with action similar to that of a shot gun. Shrapnel are usually used only in field and anti-aircraft guns.
Fuses.—Fusesare used in practically all service projectiles, to detonate, ignite or scatter the bursting charge of the projectile at the time and under the circumstances desired. Point fuses are usually used in high explosive and chemical shell to obtain quick action and burst the shell before it has penetrated the ground. Base fuses are in general used in projectiles for penetrating hard substances, such as armour plate, concrete, etc., where a point fuse would crush and fail on impact. Most fuses used in shell function upon impact, while fuses used in shrapnel and anti-aircraft shell are of the time type, which are designed to function at some pre determined time after the projectile leaves the gun and during the flight of the projectile. The time fuse used in shrapnel intended for ground targets is designed also to function upon impact. The time interval in most time fuses is obtained by means of the burn ing of a powder train, the length of which is varied by the setting of the fuse. A mechanical time fuse is one in which the desired time interval is obtained through a mechanical device rather than the burning of powder.
Theprincipal high explosives used are trinitrotoluene (TNT), picric acid, ammo nium picrate and amatol, a mixture of trinitrotoluene and ammo nium nitrate. In the case of shrapnel, however, where balls are ejected from a case, this shattering effect is not desired, and a "low explosive," such as black powder, is therefore used. In this case the time required for the explosion to be completed is relatively large as compared to the time for detonating explosives, and the heated gases, being developed more slowly, do not exercise such a disruptive effect. In the case of "high explosives," such as T.N.T., detonation is initiated by means of some highly sensitive deto nating agent such as mercury fulminate in the fuse. In the case of "low explosives," however, explosion is brought about by means of simple ignition.
Thepropelling charge, usu ally of smokeless powder (nitrocellulose, cordite, etc.), in the case of the smaller calibres of ammunition, is contained in a brass case, known as a cartridge case, which has a primer in the base to ignite the smokeless powder, and is crimped to the base of the projectile. This type of ammunition is known as "fixed ammuni tion," and is usually in calibres from 37mm. to 4.7 inches. In the case of "semi-fixed ammunition," the cartridge case is not crimped to the projectile. This type is used with howitzers where the powder charge is in the form of zoned 'bags within the cartridge case, and where it is necessary to adjust the weight of charge for different ranges. In the larger calibres of guns, where the projec tile is heavy, it would be impractical to use a complete round. The projectile, propelling charge and primer, therefore, are issued separately. In loading the gun, the projectile is first rammed to its seat and then the propelling charge is inserted. The pro pelling charge in "separate loading ammunition" consists of smoke less powder in one or more bags. Raw silk is used for these bags as this material is practically entirely consumed by the com bustion of the smokeless powder, and leaves no smoldering frag ments. In this way the danger of igniting the next propelling charge before the breech block of the gun is closed is avoided. In the case of guns, the propelling charge may be in one section or several, depending upon the weight of the complete charge. For example, since the weight of a charge for the i6-inch gun may be as much as 800lb., the charge is divided into four or six sections for ease of handling. In the case of the large calibre mortars, where various weights of charge are used to obtain various ranges, the total charge is zoned ; i.e., divided into several bags.
The primer, used to ignite the pro pelling charge of smokeless powder, is a small brass case loaded with a charge of black powder, which, in the case of the smaller calibres, is sufficient to produce efficient ignition of the propelling charge. The primer has in its head a small percussion cap which is struck by the firing pin of the gun, thus igniting the black powder charge, which in turn ignites the propelling charge. In the case of the smaller calibres, where cartridge cases are used, the primer is assembled in the head of the cartridge case. With larger cali bres, the primer is assembled in the breech mechanism of the gun. With larger calibres additional igniting powder (black powder) also is required. This is usually made up in the form of a bag attached to the rear of the propelling charge. In some of the larg est calibres this additional igniter may extend through the core or centre of the propelling charge. The size of this igniter increases with the calibre of the gun. In the case of the i6in. gun an igniter of 61b. may be used.
