A Gun is divided into five parts, which are named Cascable, First reinforce, Second reinforce, Chase, Muzzle.
The metal is made thicker towards the breech than at the muzzle, to strengthen the piece, for the elastic force of the Gunpowder is there greatest, and diminishes in power as the space it occupies is extended. The metal is made thinner towards the muzzle to make the gun lighter.
The Dispart is half the difference between the diameter of the Gun at the base ring and at the swell of the muzzle. By affixing on the muzzle a piece of metal equal to the height of the dispart, the line of sight will be made parallel to the axis of the bore, and therefore an object within point blank range can be seen. Howitzers, and some guns which have a patch or projection on the upper part of the muzzle, have no dispart, the semi-diameter of the muzzle with the patch added to it being equal to the semi-diameter of the base ring. Iron ordnance (Bloomfield’s) are intended to have a degree and a half dispart, but the founder is allowed two-tenths of an inch variation in casting Iron ordnance, for any difference which there may be between the intended and actual diameter of the base ring and muzzle.
Light Brass Field Guns 12, 6, and 3-pounders have a dispart of one degree, and Medium 12-pounders and 9-pounders have one degree and a quarter.
The Angle of dispart is the number of degrees the axis of the bore would point above the object aimed at, when laid by the surface of the gun.
Point blank range is when the piece is laid at the object without any elevation; the plane and the axis of the bore being parallel to each other. Its distance is measured from the muzzle of the piece (fired with the service charge of powder) to the first graze of the shot, or point at which it first touches the ground.
When a Shot is fired from a gun, it is acted upon by three forces:—
1st. The explosion of the Powder, which urges it forward.
2nd. The resistance of the Air, which tends to stop it.
3rd. The force of gravity, which causes it to descend.