Abstract: The invention relates to a capacity limiting assembly that provides substantially irreversible alteration of a box magazine to limit its cartridge capacity wherein the box magazine comprises a magazine housing having a vertical dimension YM, a magazine spring having at least 1 coil, and a follower. The assembly includes a limiter body and a lock plate. The limiter body has a top edge engageable with a bottom surface of the follower that is operatively associated with a top of the magazine spring extending into the cartridge reservoir and is configured to be disposed substantially within the at least one coil of the magazine spring. The limiter has a vertical dimension YL that is less than the vertical dimension YM of the magazine housing, and a limiter bottom edge that is engageable to a lock plate.