A firearm including a barrel having a breech and a muzzle defining a length of the barrel is disclosed. The firearm includes a hand guard having a first end and a second end with a front sight is attached to at least one of the barrel adjacent the muzzle and the second end of the hand guard. A housing is coupled to the front sight and defines a chamber having a piston disposed therein and movable between static and displaced positions. A receiver is coupled to the first end and a bolt carrier is disposed within the receiver and moveable between firing and rearward positions. A carrier key is attached to the bolt carrier and moves concurrently with the bolt carrier and a rod is permanently affixed to the carrier key and extends to a distal end with the piston engaging the distal end when moving to the displaced position.