NRS-1 4 shot chambered for .22LR.
This is actually a Norinco clone issued to Chinese SF's, the sheath dosn't appear to be OEM, I would expect a polymer unit similar to the AK47 bayonet.
NRS-2 single shot chambered for SP-4 ammo
NRS-3 4 shot chambered for SP-4 ammo
Some background to silent amunition:
In 1967, Aircraft Armaments Inc.(AAI) produced the Quiet Special Purpose Revolver (QSPR). In .44 Magnum calibre, this ammunition was manufactured for use by ‘tunnel rats’ in Vietnam. Using a specially modified ‘S’ series Model 29 Smith and Wesson, the cartridge fired 12 small tungsten carbide cube projectiles by way of a captured piston assembly within the case. Less than twenty Model 29s were modified by having their cylinders reamed out to accept the modified cartridge. The standard barrel was completely removed, and in its place a smoothbore ‘mud barrel’ was inserted, which had a larger inner and outer diameter. The revolver could then be safely fired with a plug of clay or mud in this shorter (about 40mm) barrel.
(From the S&W Handguns 2002 Special Collector's Edition)
While effective, the project was abandoned by the U.S. military, the Soviets however, spotted the advantages of a compact silent weapon for spec & intel operations. They adopted the design concept and developed the SP-3 silent amunition which was designed for a rifled rather than smoothbore barrel, for extended accurate range.
When the SP-3 round was fired, the protruding telescopic piston precluded it's application in an autoloading design. The SP-4 design will function in semi-automatic designs as it's cylinderical tungsten bullet also serves as the piston. The brass covered tip of the round appears to be the only section to engage the rifling. The SP-4, costs $50 to produce, is accurate out to 25M and is claimed to be armour piercing, soft armour presumably.