'Father of the PDW' Passes: Mack Gwinn Jr, Dies at 79

The firearms maverick and inventor behind the Bushmaster Arm Pistol hung up his guns for the final time this month.

Florida-born Mack W. Gwinn, Jr., the son of a retired Army officer, joined the U.S. Army Special Forces in 1961 and served until 1972, a period that included seven deployments to Vietnam, earning several Purple Hearts and the Bronze Star in the process. Shifting gears into the firearms industry post-Vietnam, Gwinn acquired the rights to the scrapped Air Force Individual Multi-Purpose weapon system, which had been prototyped as the Colt IMP-221.

The Colt-made IMP-221 was a stockless, gas-operated bullpup pistol intended to provide aircrew with a compact survival gun. Chambered in .221 Fireball, it was type-classified as the GUU-4/P by the service. Unsuccessful, the Air Force scrapped the project. Prototype SN #3 (of 5 made) is seen here in the USAF Armament Museum at Eglin AFB, Florida. (Photo: Chris Eger/Guns.com)

Redesigning the IMP-221 concept to include a caliber change to 5.56 NATO and the ability to accept standard AR magazines, Gwinn founded the Gwinn Arms company and began initial production of the Bushmaster Arm Pistol in the early 1970s. The concept, a pistol-sized firearm that used an intermediate round rather than a pistol caliber, could rightly be described as one of the first personal defense weapons and predated the initial crop of large format AR handguns such as the OA-93 by a generation.

An early Gwinn-marked Bushmaster Arm Pistol in the USAF Armament Museum. Note the design differences from the IMP-221. This gun was used in Air Force trials in the 1970s. (Photo: Chris Eger/Guns.com)

Distinctive Compact Classic: Bushmaster Arm Pistol Review

Although not a huge commercial success, the Gwinn Arms and the innovative pistol was the basis for what became Bushmaster Firearms, and the Arm Pistol remained part of the latter's logo for years.

After selling Bushmaster in 1976, Gwinn went on to take out several patents on magazines as well as design and develop concepts for numerous other firearms applications including the SSP-86 pistol.

Mark Gwinn magazine patents — Gwinn secured several firearms patents over the years, with extended capacity magazines being a recurring theme. He developed 75 and 90-round magazines for MWG Company, another of his companies.

As noted by Maine-based Hydra Weaponry-- which is run today by Mack Gwinn III-- in a statement this week on the senior Gwinn's passing:

His curiosity, intelligence, and background led him to work on a variety of projects including the Sting vehicle as a replacement for the US Army Jeep, two versions of a remote ground security vehicle, and under Ordnance Technology Inc. he created the SSP-86 target pistol with the Canon-style breach-action. Under Muzzle Lite Inc., Mack Jr. designed bull-pup stocks for the Mini 14 and the 10/22. He developed recoil reduction systems for Counter Poise. He created and sold/licensed the .50 caliber QCB system to FN. He developed 12ga. adapters for 37mm and 40mm launchers. As Firepower Inc., Gwinn Jr. developed the 75-round magazine and eventually the 90-round magazine for MWG Co.

Capt. Mack W. Gwinn, Jr. (U.S. Army, Ret.), 79, died on March 11, 2024, at the Maine Veterans' Hospital in Togus.

Donations in Gwinn's memory may be made to the Maine Veterans Project while condolences to the family may be expressed at BrookingsSmith.

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