Maxwell George Atchisson was an American engineer and firearms designer. His primary focus was the development of .22 caliber conversion kits for existing weapons, although he is perhaps best remembered today for his automatic shotgun, the AA-12.
Maxwell Atchisson was born in St. Louis, Missouri, in 1930. He was educated at the University of Missouri and then enlisted for the US Marine Corps, where he worked as a firearms instructor. After being discharged from the Marines, he worked as an engineer for the Hughes Tool Company, where he contributed to the development of experimental weapons, before joining the newly-formed Military Armament Corporation, along with Gordon Ingram and John P. Foote. While at MAC, he designed a .22 conversion kit for the M16, which proved commercially successful, and also produced a number of prototype designs which did not enter full production.
In the early 1970s, Atchisson designed a fully-automatic, 12 gauge combat shotgun known as the Atchisson Assault shotgun, or AA-12. Although it never left prototype stages during Atchisson's lifetime, the design was picked up posthumously by Military Police Systems, who began producing it in 2005.
Later in life, Atchisson designed household appliances and other non-military products. He died at the age of 72 in 2003.