Abstract: A semi-automatic gun having a gas operated device for actuating a reloading mechanism thereof. The reloading mechanism includes a cartridge magazine which extends parallel to the gun and the actuating device includes an annular piston sliding over the cartridge magazine in an annular chamber defined between the cartridge magazine and a cylinder, closed at one end, which surrounds a portion of the cartridge magazine. Gas transfer ducts convey gas from the interior of the barrel of the gun, through the wall of the cylinder into the annular chamber defined thereby. The annular piston has a peripheral groove therein at a position adjacent the gas transfer ducts so that gas entering the annular chamber impinges on the piston and not on the wall of the cartridge magazine; subsequently these gases transfer to a lower chamber between the end of the piston and the closed end of the annular chamber along a passage between the piston and the wall of the chamber itself.

Abstract: A gas-operated device for activating the reloading mechanism of an automatic rifle comprising a cylinder housing and a movable piston, both mounted coaxially upon a cartridge store, the whole assembly being affixed below the rifle barrel. Gases from a cartridge exploded in the rifle breech are bled from the barrel through a duct into an annular chamber between the piston and a closed end of the cylinder to drive the piston and activate the reloading mechanism. Immediately prior to this bleeding, gases are bled through an additional duct into an interstice between the piston and the cylinder to act as a `gaseous diaphragm` preventing leakage of the driving gases from the annular chamber, except when the pressure of these driving gases is excessively high.