of firearms using the cartridge case as a piston were known since the 1930s and still unsolved. Limited-utility designs Blish lock The Blish Lock is a breech locking mechanism designed by John Bell Blish 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 called static friction, or stiction. His locking mechanism was used in the Thompson submachine gun, Autorifle and Autocarbine designs. This dubious principle was later eliminated as redundant in the M1 and M1A1 versions of the submachine guns at the insistence of the US Army. Lubrication or fouling would completely defeat any delay. Whatever actual advantage a clean, unlubricated Blish system could impart could also be attained by adding a mere ounce of mass to the bolt. Savage rotating barrel The Savage system employed the theory that the rifling in the barrel caused a rotational force that would hold the gun locked until the projectile left the barrel. It was later discovered that the bullet had left the barrel long before any locking could occur. Savage pistols were in fact operating as simple blow back firearms. The French MAB PA-15 and PA-8 9mm pistols feature a similar design and work correctly. Headspace actuated unlocking An unusual operation that uses a bolt head that moves rearwards when firing that allows the cartridge to move backwards or even stretching it until the bolt unlocks. When firing the cartridge moves the bolt head rearwards around 2.5mm until it stops, then rotates the bolt to unlock and cycle the operation. Magnet delay An operation using a "simple blowback" type bolt that has neodymium magnets to delay its operation. A special buffer using this operation has been developed by TACCOM. Other autoloading systems Other autoloading systems are: Blow forward, which is similar to blowback, but with the whole barrel being pushed forward rather than the bolt pushed back. Recoil operation uses the rearward movement of parts of the weapon counter to the ejecta (bullet and propellant) moving forward, as described by Newton's third law of motion. Gas-operated reloading See also List of blow forward firearms List of delayed-blowback firearms List of API blowback firearms References Bibliography Bremner, Derek, The MG42V and the Origins of Delayed Blowback Roller Lock: WWII German Equipment (Paperback). . External links How Does it Work: Blowback Action Forgotten