Blish lock
Encyclopedia
The Blish Lock is a breech
Breech-loading weapon
A breech-loading weapon is a firearm in which the cartridge or shell is inserted or loaded into a chamber integral to the rear portion of a barrel....

 locking mechanism designed by John Bell Blish
John Bell Blish
John Bell Blish Known mostly for inventing the Blish lock, used in the Thompson submachine gun. Blish licensed the patent for his lock to the Auto-Ordnance Corporation in 1915 in trade for company stock....

 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 extreme manifestation of what is now called static friction, or stiction
Stiction
Stiction is the static friction that needs to be overcome to enable relative motion of stationary objects in contact. The term is a portmanteau of the term "static friction", perhaps also influenced by the verb "stick"....

. His locking mechanism was used first in the Thompson submachine gun
Thompson submachine gun
The Thompson is an American submachine gun, invented by John T. Thompson in 1919, that became infamous during the Prohibition era. It was a common sight in the media of the time, being used by both law enforcement officers and criminals...

.

The Blish Lock was the result of observations made by Blish of large naval guns. Blish observed that the breech blocks of naval guns with interrupted thread breechs remained closed when fired with full charges but tended to unscrew when fired with light charges. Using his mathematical and analytical training, 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. It did not take Blish very long to put this knowledge to use in a delayed-blowback
Blowback (arms)
Blowback is a system of operation for self-loading firearms that obtains energy from the motion of the cartridge case as it is pushed to the rear by expanding gases created by the ignition of the propellant charge....

 breech lock. He developed a working model that used a simple wedge as the lock, and was eventually assigned on March 9, 1915.

The most famous applications of the Blish Lock were the Thompson Autorifle
Thompson Autorifle
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....

 and Thompson submachine gun
Thompson submachine gun
The Thompson is an American submachine gun, invented by John T. Thompson in 1919, that became infamous during the Prohibition era. It was a common sight in the media of the time, being used by both law enforcement officers and criminals...

. However, several engineers suspected the autorifle functioned more as a retarded blowback than as an adhesion locked breech action. Some authorities, such as Julian Hatcher
Julian Hatcher
Julian Sommerville Hatcher , was a noted firearms expert and author of the early twentieth century. He is credited with several technical books and articles relating to military firearms, ballistics, and autoloading weapons...

, 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 submachinegun the "H" shaped bronze lock connects the bolt actuator to the bolt body; incorrect installation of the Blish lock can render a Thompson inoperable.

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