Mack Gwinn was a US Army Special Forces officer in Vietnam (he retired from the service as a Captain) who had extensive experience carrying and using a Stoner 63A. When he returned home, he decided to get into the firearms industry. His first work was the Ranger 7, an improvement on John Foote's FAC-70, but this did not see production. What did get into production was his Bushmaster Assault Rifle, a long-stroke gas piston rifle with an AR style bolt and fire control group, apparently inspired by elements of the Stoner. The design was sound (and fairly simple), but unfortunately the manufacturing was quite crude.

The Bushmaster was originally produced by Gwinn Firearms, until it was transferred to a company called Quality Parts, which renamed itself Bushmaster Firearms in the process. The example we are looking at today is a Bushmaster-production one. Eventually production of the Assault Rifle ceased, and Bushmaster became much better known for making AR-15 rifles. Gwinn remained in the industry, designing a number of significant items including a QD barrel system for the Browning M2 for FN, a drum magazine for the AR and Mini-14, and most recently the MGI Hydra modular barrel system for the AR.