A gas-operated firearm with a lock housing, a guide rod projecting forward from the lock housing, as seen in the shooting direction, for a lock activation device, which is located so it can be displaced on the guide rod and which interacts with a lock for its movement between a locking position and an unlocking position, and a barrel with a gas withdrawal block fastened on the lock housing, which contains at least one gas withdrawal borehole that opens into the barrel, and a pressure piston that is guided so that it can be displaced in the gas withdrawal block for the displacement of the lock activation device against the force of a lock spring. A simplified installation and dismantling of the barrel can thus be made possible in that the barrel contains a rear part, which can be placed on the lock housing and can be firmly connected with it, and a front part, which freely projects from the lock housing, without a firm connection with the guide rod.