Fig. 83.
THE BREECH-PIECE.
This is a cast-iron block, the front half solid and pierced with the channels necessary for feeding, loading, firing, and extracting ammunition, and the rear half hollow to form a chamber for the mechanism, with guideways and journals for its movement and support. In the upper front face a channelway is cut from the loading-hole around almost to the firing-point, the bottom being inclined so that as the cartridge moves along it during the revolution of the barrels it is pushed forward and close home.
The forward face is reinforced at the firing-point by a steel face-plate countersunk in it, through which the firing-pin hole is pierced. The seat for the pin-wheel is in the rear face of the solid part. This pin-wheel can only be mounted on the main shaft after the end of the latter has been inserted in its journal; and in order to put the locking-pin of the pin-wheel in place it is necessary to have a hole pierced radially from the outside of the breech-piece. This hole is kept constantly closed by a tap-screw. The rear end of the breech-piece is closed by a bronze door, hinged at the bottom, and secured by a screw-bolt at the top. On the outer sides of the breech-piece shoulders are cast to form seats for the shafts of the frame.
As the worm-shaft does not extend completely across the chamber of the breech-piece, a small journal-seat is cast just to the left of the centre of the chamber. In the right lower corner of the chamber is a guideway for the firing-bolt; on the left side is a slotway for the extractor; a small journal is pierced through the side for a cog-wheel, which is held in place by a keep-pin. In the left upper corner is a guideway for the loading-piston.
THE MECHANISM.
The work of the mechanism consists in revolving the barrels, loading, firing, and extracting.
The revolution of the barrels is a simple gear movement. The loading and extracting are reciprocal movements; that is, while a cartridge is being pushed into one barrel an empty cartridge-case is being drawn from another. The firing is accomplished by the firing-bolt, which is drawn backward by its cocking-arm pressing on the cam of the worm-wheel, and then thrown violently forward by the mainspring, when the arm drops from the end of the cam. The piece has the ordinary trigger arrangement.
In order to keep the cartridges from crowding down upon the loading-piston a small feed-gate is hung loosely in the feeding-hole. In the forward movement of the piston a small nib at its forward end catches behind the gate and lifts it up, thus cutting off the feed.