Korobov TKB-517

 Korobov TKB-517 assault rifle. The small "tube" above the barrel is a cleaning rod.

Caliber: 7.62x39mm M43
Action: Delayed blowback
Overall length: mm
Barrel length: mm
Weight: kg
Rate of fire: rounds per minute
Magazine capacity: 30 rounds

German A. Korobov, Russian gun designer from Tula, began the development of assault rifles soon after the World War Two,when he designed the TKB-408 bullpup rifle for 1946-47Soviet Army trials. Despite the failure of TKB-408, Korobov continued the development of various assault rifles, both in bullpup and traditional configurations. During late 1940s, he tried gas delayed blowback action in his series of TKB-454 experimental assault rifles, all chambered for standard issue 7.62×39 ammunition. While these rifles displayed some good results in accuracy department, these  also showed insufficient reliability. By the 1952, Korobov switched to the Kiraly-type retarded blowback action, with the two-part bolt that uses braking action of the lever, interposed between boltparts and receiver. This action allowed for significant increase of accuracy, as well as simplification of design and production, compared to then-standard KalashnikovAK assault rifles. 

During mid-1950s, Soviet Army initiates newtrials for improved assault rifle design in the same 7.62×39 M43 caliber.Korobov submits his improved TKB-517 rifle, still based on the Kiraly typedelayed blowback action; this weapon was extensively tested against modified KalashnikovAK rifle, as well a number of other designs, and found to be superior toall. Korobov was found to be most accurate and controllable in full automaticmode (primary mode of fire, according to Soviet tactical doctrine), especiallywhen fired from the shoulder or from the hip. It was also significantly lighterand less expensive to make than modified AK. Nevertheless, Soviet Army preferred less effective, but familiar and already well established Kalashnikov AKM over the moreeffective and lighter, but entirely new design.

TKB-517 is delayed(retarded) blowback operated weapon, that uses two-part bolt system, designed prior to WW2 by Paul Kiraly of Hungary. In this system, bolt has two parts -lighter breech block with breechface and extractor, and heavier bolt carrier. A two-arm lever is interposed between these two parts; lower arm of the lever rests against the receiver when bolt is fully closed. When gun is fired, pressure in the chamber forces the cartridge case backwards and against the breech face.Bolt begins to travel back, but the lever acts as a mechanical disadvantage,transferring the short movement of the light bolt to the longer movement of the heavy bolt carrier. This action is sufficient to slow down initial movement of the breech face before the bullet leaves the barrel. Once the pressure in the barrel is low enough, the lever breaks the contact with the receiver, and therest of recoil cycle both bolt parts complete as a single unit. Similar system later has been used in the French FAMAS assault rifle.receiver of TKB-517 has been made from stamped steel, furniture was made from wood. Charging handle was attached to the bolt carrier at the right side. Safety/ fire mode selector was located above the pistol grip, also at the right side of the gun. TKB-517 used standard AK/AKM type magazines, including large-capacity 40 and 75-round ones, developed for RPK light machine gun.