7.62x42 blowback, double-action, external hammer, 6-rnd box mag. The cartridge has a piston between bullet and propellant. The propellant explodes, drives the piston forward to impell the bullet; the piston is arrested by the cartridge shoulder. The noise is retained inside the cartridge case.
Effective range is about 50 meters.
Its a wonderful wacky world. You think this is good, the Germans have an underwater pistol, the P-11, 7.62 x 36 which fires darts ignited electronically from a battery in the pistol grip. Heckler & Koch is thought to be the maker but they've never officially claimed responsibility.
The Russians have an underwater assault rifle, a gas operated 5.66mm selective fire with a 26 rnd box mag. The projectiles are 120mm long drag stabilized darts fired from conventional cartridge cases. It can be used above water, too. And fun for the swimming pool.