OTs-38 Stechkin silent revolver

The OTs-38 Stechkin is a 5-shot, double-action revolver, in production and service since 2002, chambered in the silent 7.62×41mm SP-4 cartridge.
Design.
The effective range of fire for the OTs-38 Stechkin is 50 m. The fired cases are kept in the cylinder, thus ensuring the absence of sound of ejected cases. The cartridge employs a captive piston, creating a gas seal so there is no flash or loud report upon discharge.
As the cartridge is rimless, the cylinder is fed via full moon clips. The SP-4 cartridges emit no report or flame because the propellant gases are retained in the case. The OTs-38 revolver is claimed to be effectively silent as the sound level of the live and dry firing is practically identical.
S&W QSPR.
This system is virtually identical to that employed by the Quiet Special Purpose Revolver (QSPR) a variant of the commercially available Smith & Wesson Model 29 .44 Magnum revolvers, rebuilt to fire specially manufactured dedicated integrally silenced ammunition:
Early prototypes had very short smooth-bore barrels with 0.40 inch (10mm) bore and matching chambers but later versions have longer barrels of up to four inches (100mm). QSPR ammunition (which pioneered the captive piston propellant gas containment system) ejected fifteen tungsten balls from the special cartridges, weighing 7.5 grain (0.5 grams) each, exiting at a muzzle velocity of around 730 fps (222ms) for a muzzle energy of roughly 135 ft-lbs (185J).
This load was tailored to wound at up to 100 ft (30m), and have a practical, and potentially fatal, effect at ranges below 30 ft (10m), deemed sufficient for the QSPR's intended and narrow application: clearing the confined and dimly-lit to pitch-black tunnels encountered by "tunnel rats" during the Vietnam War. No sights were fitted.
The acoustic signature of QSPR rounds was around 110 dB (similar to a traditionally silenced .22LR pistol), the captive piston totally eliminated muzzle flash (vital when most engagements occurred in near or total darkness). While effective, only 250 QSPRs were manufactured; production was discontinued after the US withdrawal from Vietnam.
OTs-38.
In contrast to its virtually stock predecessor the later OTs-38 is innovative to a degree unusual even in special purpose weapons:
The OTs-38 is fitted with an integral laser sight located above the cylinder axis (where a conventional revolver has its barrel) powered by three D-0.03D batteries.