The horizontal movement of the breech-block is limited by the stop-bolt, which, passing through the breech of the gun, engages in a guide in the upper part of the block. In the right end of the breech-block is mounted a shaft on which is secured the locking-screw, and which terminates in a handle for manœuvring. The thread of the locking-screw is cut away for about 100°, in such a manner that the breech-block may be locked or unlocked by a half-turn of the handle. The =Extractor= is a single piece of steel working in a longitudinal groove in the top of the breech-mortise. Its forward end is formed into a claw to grasp the head of the cartridge. On the same side as the claw is a stud which, following a groove in the top of the breech-block, imparts motion to the extractor. The =Vent= is a cylindrical channel passing diagonally through the breech and breech-block, and changing direction in the block so as to follow the axis of the bore. The friction-primer cannot be inserted until the two parts of the vent are in prolongation from the complete closing and locking of the breech-block. The ordinary friction-primer is used. NOMENCLATURE. =The Mechanism.=--(_b_) breech-block; loading-hole; (_s_) stop-bolt; spring washer; (_r_) stop-bolt guide; (_e_) extractor; (_h_) extractor-hook; (_a k_) extractor-guide; (_c_) locking-screw; locking-screw shaft; locking-screw pin; (_l_) handle; stop; stop keep-screw. [Illustration: FIG. 3.] ACTION OF THE MECHANISM. The gun having been fired, the handle is turned to the rear, unlocking the block and starting it in the mortise. Drawing the handle smartly to the right, the breech is opened, the extractor, actuated by the movement of the block, commences to move very slowly back with a powerful leverage, starting the cartridge-case from its seat. When the breech-block has moved sufficiently to unmask the bore, the change of direction in the extractor-guide causes the extractor to make a quick movement to the rear, throwing the cartridge clear of the gun. A new charge being inserted, it is pushed home until the head of the cartridge brings up against the extractor. The breech is now closed by pushing it smartly to the left, and is locked by turning the handle to the front. A primer may now be inserted in the vent, and the gun is ready for firing. DIRECTIONS FOR DISMOUNTING THE MECHANISM. Unscrew the stop-bolt about four turns, or remove completely. Withdraw breech-block. Remove extractor, which is now free. In general nothing further need be dismounted for cleaning and inspection. To dismount completely continue as follows: Remove locking-screw pin with screw-driver. Remove stop keep-screw. Drive out stop with the drift, interposing a bit of wood or leather to avoid bruising the stop. Withdraw handle and locking-screw shaft. Remove locking-screw. To mount, proceed in reverse order.