During the 1970's the weapon was reconfigured as a commercially available .223 semi-automatic pistol. Initially sold by Gwinn Firearms with an aluminum upper receiver, later pistols manufactured by Bushmaster featured a steel upper receiver.
The Bushmaster pistol was unique in that it accepted standard AR15 magazines. The entire receiver would swivel depending if you were right or left handed. Essentially you would have the magazine lay over your arm to help steady the weapon, and ensure brass would be ejected away from your body.
While the design clearly has a coolness factor, in practice this was a very heavy design that wasn't entirely reliable. But it definately made up with it's firepower - 30rds of .223 in a very compact package.
Magazine: Uses standard AR15 magazines
Overall Length 20.6 inches
Barrel Length 11.6 inches
Rifling 1 turn in 10"
Weight w/o Magazine 5.25 Lbs.
Mode of Operation Gas Operated Semi-Automatic
Once Bushmaster switched over to making AR15 style rifles, the old Bushmaster Rifle and the Arm Pistol were dropped from their catalog, though as late as 1994 they still advertized some spare parts for these weapons.
It's amazing to look back and see what you could legally manufacture during the 1970's here in the United States. Imagine the gun ban lobby wasn't very happy to find out this kind of weapon was legally available over the counter here in the USA. Today the 50oz rule limits .223 AR15 based semi-automatic pistol designs.