The Bushmaster arm gun was produced in the late 1970s after the cancellation of the Colt IMP; Mack Gwinn Jr. obtained the patent rights to the IMP and produced it under his own company, the Gwinn Firearms Co. It was manufactured in two variants: a semi-automatic version and a selective-fire version, marketed as a "pistol" and a "submachine gun" respectively. The Bushmaster saw some limited domestic and export sales but was never produced in large quantities.
The Bushmaster was a gas-operated, selective-fire assault carbine that fired from a closed bolt. It utilized a conventional gas piston and rotating bolt mechanism with seven locking lugs. Unlike the IMP it was adapted from, the Bushmaster was chambered for the intermediate 5.56×45mm cartridge.
The trigger group and pistol grip are not fixed and can be rotated at a 40° angle to the left or right; this is intended to solve the issue of the directly upwards ejected brass casings hitting the user. When the pistol grip is rotated to the side, holding the pistol grip vertically will tilt the receiver and point the upwards ejection port to the side of the user, allowing the user to brace the rear of the gun against their body without fear for the ejected brass hitting themselves. Rotating the trigger group also tilts the front sight to the sides; the rear sight can be manually rotated to the side to accommodate for it.
An aforementioned semi-automatic version was also produced. There are at least three known variations of the design.