A carcass is a thick shell which has three additional holes of the same dimensions as the fuse-hole, pierced at equal distances apart in its upper hemisphere, their exterior openings being tangent to the great circk perpendicular to the axis of the fuse-hole. The object of a carcass is to set fire to wooden structures by the flame of an incendiary composition issuing from the holes. This shell has no fuse, and it is not intended to be exploded, although a charge of powder may be placed beneath the composition to prevent it from being approached by the enemy.
A stand of grape-shot is composed of nine small cast-iron balls, disposed in three balls each. The diameter of the balls for grape shot varies with the size of the piece; being used at long distances, they are larger than the shot for the corresponding canister. Grape shot are employed only in the siege and sea coast services; as now constructed, they cannot be used in rifled pieces.
The envelope for a stand of canister-shot consists of a tin cylinder, closed at the bottom by a thick plate of cast-iron, and at the top by one of sheet-iron. The plates are kept in place by cutting the ends of the cylinders in strips about OS inch long, which are turned down over the plates. A wire handle is at tached to the top plate. To give more solidity to the mass and to prevent the contained balls from crowding upon each other when the piece is fired, the interstices are closely packed with sawdust. For a gun 27 small cast-iron balls are used, arranged in four layers, the top of six and the remainder of seven each; this makes the diameter of the balls about one-third that of the bore. For howitzers the envelope contains 48 balls, in four layers of 12 each, the balls being smaller than those in a canister for the corresponding gun. Grape-shot and canister are no longer or seldom used, having been dis placed by shrapneL Shrapnel are cast-iron shells, in which, be sides the bursting charge of powder, is placed a number of sm 11 balls. Their sides are much thinner than those of ordinary shells in order that they may contain a greater number of bul lets; the thickness must be such that, when supported by the bullets, the case will not be broken by the force of discharge, but will yield readily to a small bursting charge. The weight of the case, empty, is about one-half, and, when filled, abopt equal to that of the solid shot of the same diameter. This projectile is prepared by filling the case with leaden musket-balls well packed in; the interstices are then filled with melted rosin; this prevents the fracture of the envelope by the bullets when the piece is fired. The chamber for the powder is after
ward bored out. The case is strengthened by a reinforce, and to increase the effect of the bursting-charge, the lower portion of the fuse hole is closed by a disc of wrought-iron, per forated with a small hole for the passage of the flame from the fuse. A shrapnel may be made to explode at any point of its flight, and, as the bursting-charge should be only sufficient to open the envelope, without scattering the bullets too much, the execution depends on the velocity which the case has at the moment it is broken.
The advantages to be derived from the use of elongated projectiles having once been es tablished, it became necessary that some means should be decided to make their flight accurate. It has been found that to do this with certainty a motion of rotation about its longer axis must be communicated to the projectile, and this end has been satisfactorily attained only by cutting spiral or °rifles) in the surface of the bore of the piece, with which the projectile is connected, and by means of which it starts with a motion about an axis parallel to or coin cident with that of the bore. The rotation con tinues during the flight of the projectile. With out this rotation an elongated projectile will naturally turn over end for end and present a constantly varying surface to the resistance of the air. This wrifle-motion,D therefore, tends to cause the projectile to move through the air in the direction of least resistance, thereby in creasing the range and the effect of impact, and, furthermore, giving steadiness to the pro jectile by distributing the deviating forces uni formly around its line of flight. The more important advantages of elongated projectiles are that the form may be altered at any time, and the centre of gravity can be placed at any desired point; the projectile may be elongated so as to oppose, for an equal weight, a dimin ished surface to any resting medium; by this the range is extended, and a flatter trajectory with greater accuracy and penetration obtained. The chief disadvantages are increased strain on the gun; greater probability of jamming and in jury to the bore irregularity of ricochet; increased complication and expense of manufac ture and the liability of any soft metal on the exterior to be accidentally injured.