Breech Mechanism

The mechanism used for opening and closing the breech of a fire-arm and securing it against the escape of the gas. In small-arms this is readily accomplished. The use of the metallic cartridge-case renders any special gas-check unnece ary, as the case itself by being expanded against the walls of the chamber serves the purpose. The various mechanisms used in small-arms have been cla ified as follows: 1st, Fixed chamber ; 2d, Movable chamber . The second cla is now obsolete. The fixed chamber cla is subdivided into—1st, Barrel moves ; 2d, Breech-block moves . The first cla comprises many of the shot-guns in use, the second, the best known of military arms . Under this latter cla are the following subdivisions: 1st, Sliding block ; 2d, Sliding and rotating ; 3d, Rotating about an axis. We find excellent guns under each of these cla es which are further subdivided as to the direction of the motions. The Sharps’ may be taken as typical of the first of these cla es, the Hotch ki magazine gun of the second, and the Springfield of the third. A similar cla ification may be made for breech-loading devices in heavy ordnance , but the problem here is not so simple. The pre ure is much greater, the ma es of metal much larger, and the cartridge must be used without a case to check the gas. Breech-loaders were impo ible until the problem of checking the gas had been solved. The inventor of the first succe ful gas-check was an American, L. W. Broad well, now residing abroad. The term Broad well ring has been applied to all similar devices. This is a steel ring which fits in a rece reamed out in the rear of the chamber and abutting upon the breech-block. The inside of the ring is so shaped as to be pre ed by the gas outwards and backwards, thus closing both the space outside of the ring and between it and the block. Broad well is also the inventor of a breech mechanism which, with a few modifications, is that used by Krupp for all of his guns. The breech-block slides horizontally through a rectangular slot in rear of the chamber. In the Armstrong breech-loader , the block called the vent-piece is taken out and put in through a rectangular orifice on the top of the gun. It is locked in place by a hollow breech-screw. The French use a breech-screw with the threads cut away in longitudinal rows. The female-screw being similarly arranged, a very small rotation enables it to be entirely withdrawn. Among American devices are Thompson’s , a breech-block which rolls to the side and opens or closes the bore. Sutcliffe’s , a cylindrical block, with its axis parallel to the one hanging on a pin projecting from the front periphery of the hollow screw. The block is raised and locked by turning the screw, and falls into a rece below when the screw is half turned back. Mann’s , in which the gun rotates upwards about the trunnions something like a shot-gun, and many others.