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Atchisson assault shotgun / AA-12 (USA)

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

Drawing of AA-12 Atchisson assault shotgun (ca. 1985), gas operated, from original patent

Current production AA-12 shotguns
image: Soldier of Fortune magazine

	Atchisson assault shotgun, 1972	AA-12, 2006
Type	selective fire, blowback operated	selective fire, gas operated, locked breech
Gauge	12 (2 3/4" Magnum)	12 (2 3/4" Magnum)
Length	991 mm	966 mm
Barrel length	457 mm	457 mm
Weight	5.2 kg less magazine 7.3 kg with loaded 20-round drum	4.76 kg less magazine
Capacity	5 rounds in box or 20 rounds in drum magazines	8 rounds in box or 20 rounds in drum magazines
Rate of fire, cyclic	360 rounds per minute	rounds per minute

American gun designer Maxwell Atchisson developed his first selective fire shotgun by 1972. This weapon was intended for close combat in environments like city streets or jungles. It was to provide tremendous short range firepower for troops during ambushes, room clearance operations and other such combat situations. First prototypes were rather simple in design and used certain components of existing weapons. These were also highly unusual in that Atchisson used most unusual (for shotgun) method of operation - simple blowback with advanced primer ignition. This shotgun fired from open bolt, and had rather heavy (1,4kg) bolt. Firing pin was movably built into bolt along with the internal pivot lever that caused the firing pin to extend and ignite the cartridge just prior to full bolt closure. To reduce peak recoil and cyclic rate of fire, Atchisson used extra-long recoil system, in which bolt after each shot recoils much further back than it is usually required to reload the weapon. Receiver of early Atchisson shotgun was made from steel tube, with attached M16-type buttstock and forearm. This shotgun also employed trigger group borrowed from Browning BAR-1918 automatic rifle, which allowed for selective semi-automatic of full-automatic fire from open bolt. Feeding was from detachable magazines, either 5-round boxes or 20-round drums. To provide necessary support for heavy drum magazines during recoil, gun was equipped with magazine support bracket that rested against pistol grip. Simple sights were of open type, with non-adjustable rear diopter and post front, both mounted on high bases.

During late 1970s and early 1980 Atchisson reworked his basic design from open bolt blowback action to more safe locked breech, gas operated action. This was done in the view of the use of more powerful, specially developed military shotgun ammunition, loaded with flechettes or heavy load of buckshot. This system employed the traditional gas chamber and piston, located above the barrel, and locking system that used single vertically sliding locking lug in the bolt head. Upon closure of the bolt, this lug was forced up to lock into the projection of the barrel. Upon discharge, gas piston forced the bolt carrier back, which, in turn, first lowered the locking lug to unlock the bolt, then carried the bolt back for reloading cycle. New weapon retained the long bolt travel, but had more conventional hammer-fired trigger unit, and it still fired from open bolt. The stock and receiver also were redesigned; now, receiver, shoulder stock and forearm were made as a single housing, assembled from two symmetrical units, left and right. This weapon also was selective fired, and used M16-style safety / fire selector on the left side of receiver, above pistol grip.

This second generation design languished for almost two decades, but recently it has been picked up by Military Police System Co (Tennessee, USA) that offers the slightly modified AA-12 selective fired shotgun for authorized military and police users in USA. It is possible that AA-12 will be used in limited numbers by some US agencies, but so far we have no information on actual use of this awesome weapon, which traces its ancestry to late days of Vietnam war. 

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