Patent ID: 8161864

Claim:
A gas piston system for an autoloading firearm comprising: a barrel having a longitudinally-extending bullet pathway; a gas block defining a piston bore; a reduced diameter axial passageway fluidly connecting the bore with the bullet pathway for diverting combustion gas from the pathway to the bore upon discharging the firearm, the fluid passageway being axially aligned with the piston bore and positioned forward of the bore, the passageway having a closed front end and a rear end which opens rearward into the piston bore; and a piston slidably disposed in the bore for reciprocating movement, the piston including a head having an axially-extending protrusion projecting towards the passageway, the protrusion being configured for slidable insertion into the passageway, the piston being movable from a first actuation position in which the protrusion is inserted into the passageway to a second actuation position in which the protrusion is at least partially withdrawn from the passageway; wherein the protrusion blocks flow of combustion gas from the passageway to the piston bore when the piston is in the first position.