=The breechblock= is the Nordenfeld rotating type, cylindrical with seven threads which serve to screw it into the rear of the breech. The breech is opened and closed by rotating the block 120 degrees around its axis. The block advances during the rotation due to the pitch of its threads and forces the cartridge case into the bore. The gun cannot be fired until the block has been completely closed, a condition which must exist before the striker of the firing mechanism is in line with the primer cartridge of the projectile. =The extractor= consists of three parts: 1. Two arms connected by a hollow shaft. 2. A spindle which passes through the shaft and fastens it to the breech. 3. An extractor tang. =The action of the extractor= is as follows: When the breech is closed the arms of the extractor are pressed against the face of the tube by the rim of the cartridge case which bears against them. The extractor tang projects into a groove in the inner face of the breechblock known as the loading groove. This groove is circular and its depth is equal to the projection of the extractor tang. It terminates in a helical guide surface called the “ejecting ramp.” [Illustration: 75 M.M. FIELD GUN MODEL OF 1897 (FRENCH)] The first part of the movement of opening the breech serves to move the grooves in front of the extractor tang. This pressure forces the extractor tang back into its slot in the breech hoop and as the extractor tang is firmly seated in the extractor, the arms of the latter are rotated around the extractor spindle. The arms being brought to the rear, press against the rim of the cartridge case, which is thereby started and ejected. Inversely (the breech being open) when a cartridge case is smartly inserted in the chamber the rim carries the arms of the extractor forward. The extractor tang is thereby forced against the beveled surface of the ejecting ramp and automatically starts the closing movement of the breechblock. A safety catch is provided to keep the breech locked between the time that the breech is closed and the shot is fired. =The firing mechanism= consists of a striker or firing pin seated in the breechblock, a firing hammer, firing rack, spring and lanyard. By pulling the lanyard the hammer is drawn back and the rack moves forward against the compression of the spring due to its being geared to the hammer. When the lanyard is released, the spring forces the rack back which in turn causes the hammer to fly forward and strike the primer. A safety device is provided for locking the hammer while the piece is in the traveling position. THE CARRIAGE.