Little is known in the Western world of the Soviet silent pistols utilizing special silent ammunition. The package consists of the model PSS (Pistolet Sptsialnyj Samozaryadnyj) silent pistol and the special SP-4 captive piston ammunition. The testing performed consisted of evaluation of the basic handgun, the special ammunition, sound pressure measurements, muzzle velocity, and terminal performance.
Give Philip H. Dater’s article a read. Very interesting. I was impressed.