The Blish lock is a

breech Breech may refer to: * Breech (firearms), the opening at the rear of a gun barrel where the cartridge is inserted in a breech-loading weapon * breech, the lower part of a pulley block * breech, the penetration of a boiler where exhaust gases leav ...

locking mechanism designed by

John Bell Blish John Bell Blish (September 8, 1860 – December 22, 1921) was an American inventor known primarily for developing the Blish lock, used in the Thompson submachine gun, more commonly known as the "Tommy Gun." Blish licensed the patent for his lock to ...

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 engineering terminology, it is an extreme manifestation of what is now called static friction, or ''

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 words ''static'' and ''friction'', and is perhaps also influenced by the verb '' to stick''. Any ...

''. His locking mechanism was used first in the

Thompson submachine gun The Thompson submachine gun (also known as the "Tommy Gun", "Chicago Typewriter", "Chicago Piano", “Trench Sweeper” or "Trench Broom") is a blowback-operated, air-cooled, magazine-fed selective-fire submachine gun, invented by United Stat ...

. Nowadays it is discredited as a useful firearm operating principle, due to its almost nonexistent effects on the operation and functioning of a firearm; because of that, firearms which theoretically employed it operate not by the supposed ''Blish lock'' principle, but, in fact, by blowback operation.

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 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

delayed-blowback 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 gas created by the ignition of the propellant charge. Several blowback systems exist wi ...

breech mechanism. He developed a working model that used a simple wedge as the delay mechanism, and was eventually assigned on March 9, 1915. Despite the patent and use of the system in the

, the Blish principle found little scientific backing. 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 The .45 ACP ( Automatic Colt Pistol) or .45 Auto (11.43×23mm) is a rimless straight-walled handgun cartridge designed by John Moses Browning in 1904, for use in his prototype Colt semi-automatic pistol. After successful military trials, it ...

cartridge. The Blish principle did provide delay in the Thompson prototypes using the

.45 Remington–Thompson The .45 Remington–Thompson was an experimental firearms cartridge designed by Remington Arms Remington Arms Company, LLC was an American manufacturer of firearms and ammunition, now broken into two companies, each bearing the Remington nam ...

and

.30 Carbine The .30 Carbine (7.62×33mm) is a rimless carbine/rifle cartridge used in the M1 carbine introduced in the 1940s. It is a light rifle round designed to be fired from the M1 carbine's 18-inch (458 mm) barrel. History Shortly before World W ...

cartridges which generate higher pressure than the .45 ACP, a pistol round. With high power rifle cartridges such as

.30-06 Springfield The .30-06 Springfield cartridge (pronounced "thirty- aught-six" ), 7.62×63mm in metric notation, and called the .30 Gov't '06 by Winchester, was introduced to the United States Army in 1906 and later standardized; it remained in military use ...

, 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 was

, and also the

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 7.62×54mmR Russian rifle rounds. Several prototypes of the Autorifle were submitted ...

. Several engineers suspected the autorifle functioned more as a delayed blowback than as an adhesion-locked breech action.Julian S. Hatcher, ''Hatcher's Notebook'', Military Service Publishing Co., 1947, pages 44-46. Some authorities, such as

Julian Hatcher Julian Sommerville Hatcher (June 26, 1888 – December 4, 1963), was a U.S. Army major general, noted firearms expert and author of the early twentieth century. He is credited with several technical books and articles relating to military ...

, 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

{{reflist

External links

The Unofficial Tommy Gun Page

Firearm actions