F41A—FUNCTIONAL FEATURES OR DETAILS COMMON TO BOTH SMALLARMS AND ORDNANCE, e.g. CANNONS; MOUNTINGS FOR SMALLARMS OR ORDNANCE
F41A5/00—Mechanisms or systems operated by propellant charge energy for automatically opening the lock
F41A5/18—Mechanisms or systems operated by propellant charge energy for automatically opening the lock gas-operated
F41A5/20—Mechanisms or systems operated by propellant charge energy for automatically opening the lock gas-operated using a gas piston arranged concentrically around the barrel