AA-12 (Auto Assault-12)


Combat Shotgun

Place of origin

United States


Maxwell Atchisson, further developed by Military Police Systems, Inc.


original 1972, 2005 MPS version



Feed System

8 rounds in box magazine, 20 or 32 rounds in drum magazines

The Auto Assault-12 (AA-12) (originally designed and known as the Atchisson Assault Shotgun) is a shotgun developed in 1972 by Maxwell Atchisson. The current 2005 version has been developed over 18 years since the patent was sold to Military Police Systems, Inc. The original design was the basis of several later weapons, including the USAS-12 combat shotgun. The weapon is selective fire, operating as a semi-automatic, or in fully automatic mode at 300 rounds per minute. It is fed from either an 8-shell box magazine, or a 20 or 32-shell drum magazine.


The designer, Maxwell Atchisson, made "over 200 tiny changes." To produce the AA-12, as we know it today.

The changes from the MPS version are:

The weapon was lightened to 4.76 kg and shortened to 966 mm but retained the same barrel length. The CQB model h

Atchisson assault shotgun (ca. 1972), blowback operated, with 20-round drum magazine

as a 13-inch barrel, and is half a pound lighter than the regular model. Uncommon in other automatic shotguns, the AA-12 fires from an open bolt, a feature more commonly found in heavy and squad level machine guns. It uses 8-round box, 20-round drum, or 32-round drum magazines, as opposed to the original 5-round box magazine. It is designed to fire three different types of 3" 12 gauge shells: Buckshot, slug, or Frag-12 rounds. Due to the abundant use of stainless steel and the designed clearance for fouling, MPS has claimed that the weapon requires zero cleaning or lubrication. The designer states that cleaning is required after 10,000 rounds.


The AA-12 uses many different types of cartridges such as 00 buck shot, #4 bird shot, 12-bore lead slugs, or less-than-lethal rubber stun batons. It can also fire flares or special FRAG-12 18.5mm fin-stablized HE, HEAP, and sensor fused HEAB "air-burst" fragmentation shells that can detonate in mid-air.