Rifleman Basic RBE Knowledge Practice Exam

In a gas-operated rifle, the energy to cycle the action comes from propellant gas that is diverted from the bore into the action. This gas is directed into a port on the bolt carrier called the gas key. The pressure inside the gas key acts on the bolt carrier, driving it rearward to unlock, eject, chamber a new round, and then return forward. The gas key is the interface that receives the diverted gas and transmits that energy to the moving bolt carrier, making it the component that directly drives the cycling of the mechanism. The firing pin isn’t driven by the gas, and while the bolt carrier does move, it’s the gas key that channels the gas that initiates that motion.