sentences:  The PSS uses a specially developed 7.62×42mm necked round SP-4 (СП-4), the same as used for the OTs-38 Stechkin silent revolver.The cartridge contains an internal piston and a propelling charge, with the stem of the piston against the base of the bullet.On firing, the piston delivers enough impulse to project the bullet from the barrel to an effective range of 25 meters.