Exterior Form

—The exterior of cannon is generally divided into five principal parts, viz.: the breech, the first reinforce, the second reinforce, the chase, and the swell of the muzzle. The breech (see Breech ) is the thickne of metal in the prolongation of the axis of the bore, and should be at least equal to one and a quarter times the diameter of the bore; a le thickne has been found insufficient for heavy iron guns. The first reinforce (see Reinforce ) extends from the base-ring to the seat of the ball, and is the thickest part of the piece, for the reason that the pre ure of the powder is found to be greatest before the projectile is moved far from its place. In shape this reinforce was formerly made slightly conical, under the impre ion that the pre ure was greater at the vent than at the seat of the projectile; but it is now made cylindrical throughout. The thickne of bronze cannon at the seat of the charge is le than for iron guns. The second reinforce (see Reinforce ) connects the first reinforce with the chase. It is made considerably thicker than is nece ary to resist the action of the powder, in order to serve as a proper point of support for the trunnions, and to compensate for certain defects of metal liable to occur in the vicinity of the trunnions of all cast cannon, arising from the crystalline arrangement and unequal cooling of the different parts.