SHUNT SYSTEM OF RIFLIN9 is a very ingenious arrangement for securing the accu rate centering of a projectile discharged from it •rifled canon. To obtain precision of aim and range, it is absolutely essential that time axis of a projectile should, at the moment of discharge, coincide exactly with the axis of the bore. This can scarcely be obtained unless the shot fits with extreme tiehtness into the gun; and if it does"so, and the gun is a muzzle-loader, it is scarcely possible to load it. The ordinary principle has the projectile smaller than the bore, so as to pass readily into the gun, resting, of course, on the bottom of the bore. The projectile is covered with a soft metal, as lead, which expands with the pressure behind, and fits the shot tight into the grooves; but from the fact that it rested (at the commencement of the expansion) on the bottom of the bore, the axis of the shot is always below the axis of the bore. To obviate this, sir William Armstrong designed the "shunt" system, which in practice has been fouud admirably effective. In riding the gun, the groove for 14 in. from the muzzle consists of a wide, deep indentation (b in fig. 1), and at the side of it a narrow indentation of less depth a; from 14 in. to 22 in. from the muzzle, this narrow groove gradually deepens, till it attains the level of the broad groove, after which they run together for a short distance, until a shunt at c, fig. 1 narrows the whole groove on the same side as a to the original width of b. Projecting from the shell is an iron flange too high to pass the narrow groove, and still higher by its side, a narrow band of zinc or of brass studs. Each of
these passes freely along the broad deep groove of the bore. As the shot is rammed home, the twist of the rifling brings the iron flange against the edge d (fig. 1) of the broad deep groove, which enables both the flange and zinc band to pass freely until past f. (fig. 1.) where the inclined plane ends. At c, however, where the groove becomes narrowed to only the width of the flange and band together, the shot is shunted over to the left. In this position it is rammed home. In coming out, of course, the pressure of the twist is reversed, and the zinc band presses against the straight edge e; on reaching f, the force of the exploded powder behind drives the shot on, while the inclined groove from f to g flattens down the zinc band, so that the projectile ceases to lie on the bottom of the bore, and is firmly centered by its several bands on the shallow grooves (whatever their num ber may be) round the bore's circumference. The lead fitting at the back of the shot be' been meanwhile driven by the explosion into the deep wide grooves, so as to stop whit: age.
The Russians have a shunt system borrowed from sir W. Armstrong's, but differing in details. American guns, on similar principles, have been made experimentally. The invention does not appear to have been yet applied to small arms.
There is only a minute difference between the diameters of bore and projectile.