US Patent 9038304 Gun magazine

A gun magazine includes an outer shell, an inner shell mounted in the outer shell and including a top opening, a track extended from the top opening, a guide block supported on a spring member in a rear end of the track and movable in and out of the top opening, a bottom cover affixed to the inner shell and the outer shell at a bottom side, and an adjustment member including a lever inserted through an elongated slot in the bottom block, a pivot holder located at a top end of the lever and pivotally connected to the inner shell and a guide rod extended from the top end of the lever and terminating in a retaining tip that is movable in and out of the track to stop or not to stop the guide block subject to operation of the lever between two positions, thereby adjusting the bullet storage capacity of the track.