The Thompson Autorifle was a

semi-automatic rifle A semi-automatic rifle is an autoloading rifle that fires a single cartridge with each pull of the trigger, and uses part of the fired cartridge's energy to eject the case and load another cartridge into the chamber. For comparison, a bolt-a ...

that used a

Blish Lock The Blish lock is a breech locking mechanism designed by John Bell Blish based upon his assumption that under extreme pressures, certain dissimilar metals would resist movement with a force greater than friction laws would predict. In modern en ...

to delay the action of the weapon. It was chambered in .30-06, with the 1923 model in 7.62×54mmR 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 The .276 Pedersen (7×51mm) round was an experimental 7 mm cartridge developed for the United States Army. It was used in the Pedersen rifle and early versions of what would become the M1 Garand. Summary Developed in 1923 in the United S ...

, 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 The M1 Garand or M1 rifleOfficially designated as U.S. rifle, caliber .30, M1, later simply called Rifle, Caliber .30, M1, also called US Rifle, Cal. .30, M1 is a semi-automatic rifle that was the service rifle of the U.S Army during World War ...

. 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.

Function

For reloading, the Thompson Autorifle uses an

interrupted screw Breech from Russian 122 mm M1910 howitzer, modified and combined with 105 mm H37 howitzer barrel An interrupted screw or interrupted thread is a mechanical device typically used in the breech of artillery guns. It is believed to have be ...

delayed blowback operation where the bolt has 85° angled interrupted rear locking lugs that have to overcome a rotation of 110° ( 90° to unlock before the angle blend of 70°/40° and 6°) that delays the action until the gas pressure drops to a safe level to eject. The bolt cocks the striker on opening (a la Mauser) and fires from a closed position. When firing, the trigger when pulled pushes a lever connected to a sear to fire the weapon. The receiver is of a round section with the safety switch at the rear along with the rear sight. The magazine is stripper fed holding 5 rounds and lubricated by oiled pads; later prototypes used 20-round M1918 BAR magazines.

BSA Autorifle

The BSA Autorifle was a British automatic rifle designed by Birmingham Small Arms Co. This rifle was manufactured by BSA under their licensing agreement with the Auto-Ordnance Corp. It was offered for British Army trials during the 1920s.Rifles of the World, Page 579 The weapon was an improved derivative of the Thompson Autorifle that could be operated manually if the two curved 'shutters' around the bolt head are moved into the down position. By this means the mechanism is disconnected and the rifle can be used as a manual loader. This facility was a requirement in self-loaders offered for British trials at this period. The weapon took part in trials during 1927 against a Colt-made Thompson, an 'improved' BSA Thompson, a gas-operated BSA and the Farquhar Hill. Although in 1928 reports it narrowly beat the 'improved' BSA and the Farquhar Hill in the third place, it never advanced past prototype stages as none were found acceptable and development of the BSA Autorifle waned. BSA Guns Ltd, a licensee of protecting the patents of the Thompson Autorifle made a handful of the 1923 model Thompsons as 'heavy rifles' with folding bipods and finned barrels. Surviving examples suggest there were Rifle and Light Machine Gun variants and 6 of both types were manufactured. The first examples were made in 1924 and an 'improved' variant in 1926. The 'improved' BSA Thompson had a shorter operation with a straight pull cocking handle installed at the rear of a cocking sleeve. The BSA Autorifle is a delayed blowback–operated rifle chambered in the .303 British round and fed from a removable 10-round box magazine. Much like its predecessor, it uses a bolt with 85° angled threads delayed by a 90° twist to unlock from a bronze nut until the gas pressure drops to a safe level to eject. The bolt cocks the striker on opening (a la Mauser) and fires from a closed position. When firing, the trigger when pulled pushes a lever connected to a sear to fire the weapon. The receiver is of a round section with the safety switch at the rear along with the rear sight.

References

Experimental Semiautomatic Rifles 1919-31
.30-06 Springfield semi-automatic rifles 7.62×54mmR semi-automatic rifles Rifles of the United States Trial and research firearms of the United States