Abstract: A firearm adapter for AM180 .22 caliber cartridge drums includes: a tower adapted to engage with a cartridge-receiving mechanism of the firearm; a plate having a first surface to releasably engage with and retain the cartridge drum in a plane generally parallel to the plate, and a second surface to engage with and retain the tower in an orientation at a substantial angle to the plane of the plate; and an aperture in the plate that aligns with a feeding aperture in the drum and the tower so as to transport the cartridge from the drum to the tower.