fermeture

Century Dictionary and Cyclopedia

1. n. A mechanism for closing the bore or chamber of a breech-loading small-arm or cannon; a breech-closing apparatus. The Krupp fermeture consists of a cylindroprismatic wedge furnished with a Broadwell ring to serve as a gas-check. This wedge slides transversely in a mortise in the steel breech-piece, and in the large calibers it is moved in and out by a translating screw on one side. The block is locked in position by a second screw having a part of its thread cut away so that a partial turn causes it to engage or disengage in the breech of the gun. The French or interrupted-screw fermeture is a steel screw with its exterior divided into sextants or arcs of 60 each. The screw threads are removed from the alternate arcs, which thus present a plain cylindrical surface. The interior surface of the breech of the gun is similarly formed with alternate blank and threaded sectors. Inclosing, the threaded sectors on the block are brought opposite the blanks in the breech, and the block is inserted by turning a translating screw; then one sixth of a turn of the block to the right engages the threads on the block with those in the breech and closes the chamber. The De Bange or Freire gas-check is generally used with this system of fermeture. The fermeture of the Hotchkiss mountain-gun consists of a simple prismatic wedge, with a locking screw engaging in a recess in the breech. A handle on one side serves to close and draw out the block, and to lock it. This form of block has merely to support the head of the cartridge-case, which acts as its own gascheck. The fermetures for small-arms present a great variety of combinations and movements. The most important are the rotating breech-block, as in the United States Springfield and Martini-Henry rifles; the sliding breech-block, as in the Sharps and Winchester rifles; and the sliding bolt, as in the Hotchkiss and Chaffee-Reeee rifles. In all modern small-arms the metallic cartridgecase serves as a gas-check or obturator. See gas-check, in-terrupted screw (under screw), obturator, and cut under cannon.

GNU Webster's 1913

1. n. (Mil.) The mechanism for closing the breech of a breech-loading firearm, in artillery consisting principally of the breechblock, obturator, and carrier ring.