7.62 mm S-4M special compact pistol
The S4M double-barrelled over/under silent pistol was developed in the early 1970s. If is of the same type of special-purpose weapons as the MSP pistol, but is chambered for a more powerful special cartridge and differs in design.
The PZ Zmeya 'captive-piston' cartridge was developed in the mid-1960s. II features a thick-wailed case 62.8 mm long. The inside surface of the cartridge case is bottlenecked, while the outside surface is cylindrical. A special design of a percussion primer recessed deep into the case base, accommodating an extra striker, prevents the cap from bulging after the piston seals the expanding powder gases inside the case by sealing bleed-off holes. The cartridge uses the same 7.62 mm PS Mod 1943 assault rifle bullet weighing 7.9 g.
The PZ cartridge was first used in the S4 Groza pistol, followed by the S4M. The PZ round became the basis for PZA and PZAM special cartridges, differing in cartridge case design and shape.
The cartridges are fed into the chambers simultaneously using a steel two-round clop. The trigger assembly is cocked automatically, and the external finishing of the pistol prevents catching on clothes.
S-4M special compact pistol