and some countries still use cast-iron common Alen; but in the United States Navy all shells are of forged steel. The common shells have hardened points and are intended to pierce armor two-thirds of a calibre in thickness, while the armor-piercing shells are designed to pass through any thickness through which they can be driven, not only without breaking up by the shock, hut without deformation. Armor-piereing projectiles of a calibre exceeding six inches are not gen erally loaded, as their walls are so strong that gunpowder will not burst them. Several high explosives have been successfully employed for these shell:, but none has been definitely adopted for shells of all calibres. (See Exrro stvEs.) To further increase the penetrative power of armor-piercing shells. they are fitted with a soft steel cap over the point. This cap is cylindrical and about a quarter of the calibre of the shell in diameter, while its height on the outside is about equal to its diameter; inside, the point of the shell extends well up into it. When the projectile strikes a hard-faced armor plate the force of the blow, acting through the cap, slightly dishes the face of the plate and thus strains the metal; while under this strain the point of the projectile passes through the cap and easily ruptures the strained material.
In the United States and British navies shells are about calibres in length, and their weight is approximately equal to one-half of the cube of the calibre (expressed in inches). In the United States Army guns, the weights of pro jectiles are about one-sixth greater.
In addition to the two kinds of shell mentioned, shrapnel are used in modern rifled guns. espe cially- in the modern field guns, and in some pieces canister is occasionally employed. Shrap nel are shaped like shell, but have thinner walls and are filled with lead or iron bails from half an inch to an inch in diameter held in a resin The difficulties connected with developing an effective breech meehanism were soon surmount ed and modern projectiles quickly took on very nearly their present oblong shape. With breech loaders the band could be made larger than the bore (being inserted from the rear) and forced in, the lands or grooves of the rifling cutting their way through the -oft metal hand. Projectiles for breech-loading rifles were first made of plain cast iron and wrought iron. but the advances in armor brought forth first the chilled east-iron armor-piercing shot and shell. and then the steel
shell. For a long time common shells not in tended to pierce armor were made of cast iron, matrix or by metal rings. A small bursting charge, located either at. the front or rear, breaks up the ease in the air and the balls scatter and fly onward, spreading out like shot from a shotgun. In canister the balls. larger than those in shrapnel, are sunk in soft-wood disks piled up to form a cylinder, and the whole cov ered with a tin case; or. in small calibres. the halls are simply packed in sawdust and inclosed in a cylindrical tin ease with wooden ends.
In the days of smooth-bore ;runs many kinds of projectiles were used, as bar shot, chain shot, grape shot, hot shot (these were heated in special ovens), shrapnel, canister. Grape shot consisted of iron balls piled around a central spindle rising from a disk which was nearly equal in diameter to the calibre of the gam A ring of the same situ as the disk rested over the outer parts of the balls of each layer, and the next layer above rested partly in the ring. While the rings kept the halls in position, they were additionally held by a canvas cover lashed down tightly over the balls. When the gun was tired, the balls broke loose, but the rings and canvas kept them somewhat together for a considerable distance from the muzzle.
To reduce the expense of target practice (q.v.), sub-calibre ammunition is greatly used. A smaller barrel is fitted in the bore of the gun and its own projectiles used in it. In the United States Navy, one-pounder glans are fitted in the breech of guns of tive-inch calibre and larger—musket barrels being used in the smaller guns. To further decrease the cost of the prac tice, the shells are cheaply made and are blind (i.e. they have neither bursting charges nor fuses). See articles on AMMUNITION; ARMOR l'LATE; ARTILLERY; EXPLOSI WES ; FIELD ARTIL LERY; GUNS, NAVAL; BALLISTICS; GUNNERY; ORDNANCE; etc.
Btiir.1OCKAPHY. Consult: Cooke, Text Book of Ordnance and Gunnery (1S78) ; Ingersoll, Text Book on Ordnance on If G unncry (Annapolis, 1899) ; Broil', Ordnance and Gunnery (New York, 1900) ; Proceedings of time United States Naval Institute (professional notes on projectiles in every issue and numerous articles in different numbers) ; Journal of United States Artillery (Fort Monroe) ; Annual Report of the Office of Naval Intelligence (United States Navy).