Blish lock
The Blish lock is a
Invention
The Blish lock resulted from John Blish's observation of large naval guns. He noticed that the breech blocks of naval guns with
Despite the patent and use of the system in the Thompson submachine gun, the Blish principle found little scientific backing.[1] In the simplified WWII M1 Thompson re-design, the Blish locking block was removed without substantial change to the gun's function with the .45 ACP cartridge. The Blish principle did provide delay in the Thompson prototypes using the .45 Remington–Thompson and .30 Carbine cartridges which generate higher pressure than the .45 ACP, a pistol round. With high power rifle cartridges such as .30-06 Springfield, the delay offered by the Blish principle was not enough to prevent the violent ejection of fired cartridge casings being hazardous to bystanders. The autorifles developed by Thompson, Colt, and BSA in the 1920s using the Blish principle never went beyond the prototype or trial stage.
Applications
The most famous application of the Blish lock were the Thompson submachine gun and the Thompson Autorifle. Several engineers suspected the Autorifle functioned more as a delayed blowback than as an adhesion-locked breech action.[2] Some authorities, such as Julian Hatcher, felt the Blish lock as employed in the submachine gun did not accomplish much in terms of actual breech locking. In fact, the submachine gun was successfully redesigned as a simple blowback weapon (the M1/M1A1). Any real advantages to the system were far outweighed by the additional cost of manufacture associated with the device. Also, in the Thompson submachine gun the H-shaped bronze lock connects the bolt actuator to the bolt body; incorrect installation of the Blish lock can render a Thompson inoperable upon firing.
References
- ^ Matthew Moss. "The Tale of the Tommy Gun", Popular mechanics Feb 27, 2017
- ^ Julian S. Hatcher, Hatcher's Notebook, Military Service Publishing Co., 1947, pages 44-46.