A group of guns of the like design are generally given the name of their first inventor, or the place of manufacture: such as the Armstrong gun, the Vickers-Maxim, the Martini-Henry rifle, or the Enfield.
The indifferent use of several expressions in describing the same weapon is, however, rather confusing. One particular gun may be thus referred to:—by its weight in tons or cwt., as “the 35-ton gun”; by the weight of its projectile, as “a 68-pounder”; by its calibre, that is, size of bore, as “the 4-inch gun.” Of these the heavier breech-loading (B.-L.) and quick-firing (Q.-F.) guns are generally known by the size of bore; small Q.-F.’s, field-guns, &c., by the weight of projectile. It is therefore desirable to enter these particulars together when making any list of service ordnance for future reference.
No individual gun, whether large or small, is a single whole, but consists of several pieces fastened together by many clever devices.
The principal parts of a cannon are:—
(1) The chase, or main tube into which the projectile is loaded; terminating at one end in the muzzle.
(2) The breech-piece, consisting of (a) the chamber, which is bored out for a larger diameter than the chase to contain the firing-charge. (b) The breech-plug, which is closed before the charge is exploded and screwed tightly into place, sealing every aperture by means of a special device called the “obturator,” in order to prevent any gases passing out round it instead of helping to force the projectile forwards towards the muzzle.
The whole length of inside tube is termed the barrel, as in a machine-gun, rifle, or sporting-piece, but in the two latter weapons the breech-opening is closed by sliding or springing back the breech-block or bolt into firing position.
Old weapons as a rule were smooth-bored (S.-B.), firing a round missile between which and the barrel a considerable amount of the gases generated by the explosion escaped and caused loss of power, this escape of gas being known as windage.
In all modern weapons we use conical projectiles, fitted near the base with a soft copper driving-band, the diameter of which is somewhat larger than that of the bore of the gun, and cut a number of spiral grooves in the barrel. The enormous pressure generated by the explosion of the charge forces the projectile down the bore of the gun and out of the muzzle. The body of the projectile, made of steel or iron, being smaller in diameter than the bore, easily passes through, but the driving-band being of greater diameter, and being composed of soft copper, can only pass down the bore with the projectile by flowing into the grooves, thus preventing any escape of gas, and being forced to follow their twist. It therefore rotates rapidly upon its own longitudinal axis while passing down the barrel, and on leaving the muzzle two kinds of velocity have been imparted to it;—first, a velocity of motion through the air; secondly, a velocity of rotation round its axis which causes it to fly steadily onward in the required direction, i.e. a prolongation of the axis of the gun. Thus extreme velocity and penetrating power, as well as correctness of aim, are acquired.
The path of a projectile through the air is called its trajectory, and if uninterrupted its flight would continue on indefinitely in a perfectly straight line. But immediately a shot has been hurled from the gun by the explosion in its rear two other natural forces begin to act upon it:—
Gravitation, which tends to bring it to earth.