Atchisson Assault Shotgun

The Atchisson Assault Shotgun, also known as, Auto Assault-12 (AA-12) is a firearm first developed in 1972 by Maxwell Atchisson. It served as the basis of several later weapons, including the USAS-12 combat shotgun.

The weapon can fire in semi automatic or fully automatic modes.

MPS version
In 1987, Max Atchisson sold the rights of AA-12 to Jerry Baber of Military Police Systems, Inc. The company in turn developed the successor simply known as Auto Assault-12, which was redesigned with 188 changes/improvements over the original blueprint, and had taken 18 years to develop. MPS also teamed up with Action Manufacturing Company, and Special Cartridge Company to combine the gun with FRAG-12 High-Explosive ammunition into a weapon system. In 2004, 10 firing models of the AA-12 were produced, and were demonstrated to United States Marine Corps.

The weapon was shortened to 966mm but retained same barrel length as the original, and lightened to 4.76kg.

It uses an 8-round box, 20-round drum, or 40-round drum magazine. It is designed to fire three different types of 12 gauge shells: Buckshot, Slugs, or Frag-12.

MPS also claimed this gun requires zero cleaning or lubrication.

AA-12 CQB model has 13-inch barrel length, and is half a pound lighter than the regular model.

Media Coverage
The MPS version of the was featured on the March 19, 2007 episode of Future Weapons.