The breech-block has two threaded and two plain sectors (each 90 degrees) with corresponding sectors in the breech of the gun, so that the block is locked or unlocked by a quarter of a turn. The block contains a firing-pin which, with its spring, is inserted from the front end of the block, which is then closed by a threaded cap. The centre hole in this cap permits the striking end of the pin to come through to the front in certain positions of the block and to hit the primer. The rear end of the block is countersunk to receive the operating-lever, the locking-latch and its spring, the cocking-lever and its hinge-pin, the trunnioned collar, the notched cap, and the sear and its spring.
The extracting-device engages in front of the cartridge-head and grips it for more than one eighth of its circumference. Its motion is guided parallel to the axis of the piece by two cylindrical arms working in slots cut in the breech. Swinging the carrier-ring around its pivot causes the extracting-device first to act as a wedge to loosen the cartridge-case, and then by a rapid motion the case is thrown out of the gun, or far enough to the rear in the breech to be easily removed by hand.
The operation of the mechanism of the gun is as follows:
The operating-lever is seized with the left hand, and a handle on the right rear face of the carrier-ring with the right hand. The lever is pulled slightly more than 90° to the left.
The first motion of the lever unlocks the cocking-latch; the remainder of the motion rotates the block in the carrier-ring, disengaging the screw-threads. During this motion of rotation the cocking-lever has pulled back the firing-pin, which is held in position by an edge of the sear engaging under a notch on the screw-cap.
The carrier-ring is then swung to the left by the handle in the right hand.
The block moves to the left with the ring and passes partly through the slot out of the breech and uncovers the bore.
The first motion of the ring loosens the cartridge-case, as before described, and then ejects it. The new charge is then thrown in, no care being taken to seat it; the ring swung to, and the block rotated and locked.
As soon as the block is locked, pulling the sear fires the gun.