Back in the late 70’s Russia came up with a cool concept. A silent cartridge. You can see the cut away above and below. The long cylinder is the projectile and the red piece under it is the piston. When the primer is struck it ignites the powder like a conventional cartridge. The combustion pushes the piston and that pushes to projectile out. The piston is wide so it cannot get past the neck at the top. This seals the cartridge and the gas cannot escape. This results in very little noise coming from the combustion. It has been reported to have a noise level of only 110 db, similar to a suppressed sub sonic .22lr.
There are three weapons that use this cartridge. The PSS semi auto pistol, the OTs-38 revolver and the NRS knife.