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Thompson 21 and Rifle

Thompson Autorifle Model 1923 (top) and SMG Model 1921

The Thompson Autorifle was a semi-automatic rifle that used a Blish Lock to delay the action of the weapon. It was chambered in .30-06, with the 1923 model in 7.62mm Russian rifle rounds.

Several prototypes of the Autorifle were submitted by Auto-Ordnance to the military for the semi-automatic rifle trials, but it was not adopted. The Autorifle Model 1929, in .276 Pedersen, 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.

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.[1]


  1. Julian S. Hatcher, Hatcher's Notebook, MSPC 1947, pp.44-46, 155-156, 165-166.

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