Editing Blish lock (section)

== Invention ==
The Blish lock resulted from John Blish's observation of large naval guns. He noticed that the breech blocks of naval guns with [[interrupted screw|interrupted thread breeches]] remained closed when fired with full charges, but tended to unscrew when fired with light charges. He concluded that dissimilar metals have a tendency to adhere to each other when subjected to very high pressure. This principle of metallic adhesion of dissimilar metals became known as the Blish principle. Blish put this theory to use in a [[Blowback (arms)|delayed-blowback]] breech mechanism. He developed a working model that used a simple wedge as the delay mechanism, and was eventually assigned {{US patent|1131319}} on March 9, 1915. 

Despite the patent and use of the system in the [[Thompson submachine gun]], the Blish principle found little scientific backing.<ref>Matthew Moss. [https://www.popularmechanics.com/military/weapons/a25414/tommy-gun-thompson-submachine "The Tale of the Tommy Gun"], ''Popular mechanics'' Feb 27, 2017</ref> 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 [[Thompson Autorifle|autorifles]] developed by Thompson, Colt, and BSA in the 1920s using the Blish principle never went beyond the prototype or trial stage.