On the left side of the gun-case is a strong spiral spring the rear end of which is connected, by a chain and fusee, with the crank shaft, and the fore end is connected to the gun-case by means of the spring-case; this spiral spring is to bring back the barrel after the recoil and to work the crank; the working strength of the spring can be adjusted by means of the screw at the fore end. The water-jacket surrounds the barrel and is fitted with three openings, one for receiving the water, one for drawing it off, and the third for letting off the steam; the first two are closed by screw-plugs, the third is always open. Both ends of the water-jacket are fitted with stuffing-boxes and glands; these guide the barrel and prevent the escape of water. In the feed-box, on top of the gun, are two movable pawls and two stationary ones. The movable pawls are connected by a lever to the barrel and are so adjusted that the barrel on recoiling moves them from left to right; by means of a spring they engage behind the next cartridge in the belt, and thus the cartridges move on automatically towards the chamber; when the barrel returns after the recoil, the pawls place the cartridge, still in the belt, immediately above the chamber. OPERATION OF THE MECHANISM. =Cocking the Lock.=--As the lock is brought away from the breech, by the action of the crank, the connecting-rod throws down the hammer, thereby pulling back the firing-pin and compressing the mainspring, which causes the short arm of the trigger to engage under the lug of the hammer, and thus the lock is cocked and cannot act until the trigger is pulled clear of the lug on the hammer. The safety-sear, _V_, pressed down by a small spring, engages in the upper part of the firing-pin as it is drawn back by the action of the hammer; the firing-pin cannot move forward until this sear is raised; this is done by the connecting-rod, after it rises above the horizontal, thereby securely closing the breech with the lock. =Operation in Firing.=--In starting the gun the breech mechanism is operated by hand to insert the first cartridge in the barrel. The gun is then fired by pressing the firing-button. On the explosion of the cartridge the barrel and the gear connected therewith recoil about the distance of one inch. During the recoil the crank-arm comes in contact with the resistance-piece, _K_, and throws over the crank, bringing the end of the crank-handle onto the spring-buffer. The curve on the crank-arm is so arranged that the crank gets an accelerated movement by which the lock is thrown back clear of the breech and far enough for the carrier to extract the empty case from the chamber and a cartridge from the belt.