This handle (_g_) is attached to the breech-block by two screws. Its purpose is to assist in withdrawing and pushing in the breech-block. [Illustration: THE VENT-COVER. FIG. 36.] =For Axial Vent.=--A radial slot (_a_, Fig. 36) is made in the rear part of the breech-block, in which slides a piece of metal (_b_) having a pin (_c_) projecting from its forward face next the gun. This pin fits into a groove (_d_) cut in the rear face of the carrier-ring, which is eccentric at its lower end, so that when the block is placed in firing position the slide is raised and the vent uncovered. =For Radial Vent.=--This consists of a long arm, secured in position on top of the gun so that it can slide. The under side at its rear end has a slight projection, which engages over a shoulder on the lever-handle. When the lever-handle is raised a shoulder on it bears against the end of the arm, pushes it forward and covers the vent; when the block is in firing position and the lever-handle is lowered the shoulder bears against the projection and draws back the arm, thereby uncovering the vent. [Illustration: ACTION OF THE BREECH MECHANISM. FIG. 37.] Suppose the breech closed and the gun ready for firing. In this position the threads of the breech-block are engaged in the threads of the jacket (revised model) or base-ring (model '85); the gas-check is in its seat; the lower end of the latch is at the end of the transverse groove in the block; the nose of the latch is withdrawn from its recess in the jacket, and the carrier-ring is unlocked; the lever-handle is vertical, its cam in the recess in the carrier-ring, and its lower end in the recess in the jacket. =To Open the Breech.=--Grasp the lever-handle (_h_, Fig. 37) with the left hand, thumb down, and raise it until it strikes the stop, then rotate the block as far as possible to the left; lower the lever-handle: its cam (_d_), acting against the surface (_r_) of the carrier-ring, will withdraw the gas-check if it sticks in its seat. This rotation of the block pushes the latch into its recess and locks the carrier-ring to the jacket. Grasp the bronze-handle (_g_) with the right hand, thumb to the right, and withdraw the block until it comes up against the stop. In this position the stem of the latch drops into the locking-recess, locking the block to the carrier-ring, and at the same time unlocking the carrier-ring from the jacket; swing the block and carrier-ring around to the left and insert the projectile and charge.