The Thompson Autorifle was a semi-automatic rifle that used a Blish Lock

Blish lock

The Blish Lock is a breech locking mechanism designed by John Bell Blish based upon his observation that under extreme pressures, certain dissimilar metals will resist movement with a force greater than normal friction laws would predict. In modern engineering terminology, it is considered to be an...

 to delay the action of the weapon. It was chambered in .30-06

.30-06 Springfield

The .30-06 Springfield cartridge or 7.62×63mm in metric notation, was introduced to the United States Army in 1906 and standardized, and was in use until the 1960s and early 1970s. It replaced the .30-03, 6 mm Lee Navy, and .30 US Army...

, with the 1923 model in 7.62mm Russian rifle rounds.

Several prototypes of the Autorifle were submitted by Auto-Ordnance

Auto-Ordnance Company

Auto-Ordnance was a U.S. arms development firm founded by retired Colonel John T. Thompson of the U.S. Army Ordnance Department in 1916. Auto-Ordnance is best known for the Thompson submachine gun, notorious as a gangster weapon of the Roaring Twenties and famous as a military weapon of the Allied...

 to the military for the semi-automatic rifle trials, but it was not adopted. The Autorifle Model 1929, in .276 Pedersen

.276 Pedersen

The .276 Pedersen round was an experimental 7 mm cartridge developed for the U.S. Army and used in the Pedersen rifle and early versions of what would become the M1 Garand rifle.-Summary:...

, was tested in a competition with the rifles by J.D. Pedersen (delayed blowback) and John C. Garand (gas-operated), which culminated in the adoption of the M1 Garand

M1 Garand

The M1 Garand , was the first semi-automatic rifle to be generally issued to the infantry of any nation. Called "the greatest battle implement ever devised" by General George S...

.

On the positive side, the Autorifle action avoided the complexity of recoil-operated and gas-operated actions. On the negative side, the Autorifle required lubricated ammunition for proper functioning and the ejection of spent cartridge casings was so violent as to be hazardous to bystanders.