David Marshall Williams was hired by the Winchester company in 1939, and would have a hand in a number of major projects during his 10-year stint with the company, although best known for the M1 Carbine. The Carbine was an offshoot of the Winchester G30 and G30M rifles, which would also evolve into the G30R and Winchester Automatic Rifle. Another offshoot using this same basic mechanism was this undesignated .50 BMG semiautomatic antitank rifle developed by Winchester during World War II.

This rifle, like its developmental precursors, uses a two-lug, Garand type rotating bolt and a Williams gas tappet short stroke action. It has a 10-round detachable box magazine.

Although I have not found a testing report, the gun was apparently tested by the Canadian military and performed quite well. It was never purchased or put into serial production, however, most likely because as an antitank rifle the .50 BMG cartridge was not effective by the end of World War II.