The principal parts are: the spindle (a); the front cup (f); the rear cup (f′); the pad (g); the spring (j); the nut (h); the spline-screw (k).
The spindle has a mushroom-shaped head (b), and a stem, which extends through the breech-block and terminates in a screw-thread. The breech-block is recessed correspondingly. In guns with axial vents, the vent (c), 0.2 inch in diameter, passes through the axis of the spindle, and the copper bushing (d) is inserted by pressure at the front end.
The front and rear gas-check cups are of steel, and hold between them a plastic pad made of certain proportions of asbestos and tallow and covered with canvas (with disks of copper (m) on either side in the revised model,) and a diagonally-split ring (n) of steel is used to cut off the escape of gas.
A spiral spring (j) surrounds the stem of the obturator at the rear of the block, and bears against a shoulder on the block and a nut (h) on the screw-thread of the spindle. This spring, which acts to press the spindle back, keeps the cups and pad in place, takes up any set of the pad due to firing, and prevents the fracture of the screwed end of the stem.
The spline-screw (k) holds the nut on the spindle in position and prevents its unscrewing when the pad sticks in its seat after firing.
THE FREYRE OBTURATOR.
Fig. 35.
The principal parts are ([Fig. 35]): the spindle (a); the gas-check ring (f); the spring (e); the obturator-nut (d); the locking-nut (d′), or the spline-screw.