The Bushmaster Arm Pistol is an American bullpup pistol.
The weapon was first made in 1977, with a similar design being the Colt IMP-221, which used a much smaller caliber than the Arm Pistol, which was .221 Remington Fireball. The Arm Pistol ceased production in 1991, after Bushmaster was acquired by the Quality Products Company the previous year.
The Arm Pistol most probably uses a gas piston system. It can either be considered a short rifle or a long pistol.