BULLET WEIGHT – 0.49 g (7.5 grains) each, 15 pellets per load – 7.3 g (112.5 grains)
CASING WEIGHT – 29.87 g (461 grains)
TOTAL ROUND WEIGHT – 38.6 g (606 grains)
MUZZLE VELOCITY – 229 m/s (750 fps)
NOMINAL BARREL LENGTH – n/a
MUZZLE ENERGY – 13 j (9 ft/lb) per pellet, 191 j (141 ft/lb) per load
This was a series of round manufactured for the Smith & Wesson Tunnel Weapon, a highly converted S&W Model 29 revolver. The original round was known as the Tunnel Weapon round as the weapon and ammunition was intended for the use of Tunnel Rats in Vietnam. The Tunnel Rat would go underground to root out the Viet Cong in their tunnel hideaways. The Tunnel Weapon was intended to give these men a weapon with a minimum flash and noise signature while also acting as a short-range shotgun. The cartridge fired a plastic sabot containing 15 pellets of tungsten alloy. The sabot was destroyed as it left the cartridge so the pellets would leave a very short barrel with a muzzle velocity determined by the cartridge. Inside of the cartridge, a pistol would seal off the propellant gases and propel the sabot and pellet forward. A heavily-threaded end on the bore of the cartridge case would capture the piston. With the piston held in place, now propellant gases left the cartridge, minimizing noise to little more than the mechanical sound of the revolver operating.
Besides being used for its original intended purpose by the Tunnel Rats, a small number of the Tunnel Weapons were used in the field. The revolvers would be used to initiate an ambush, or, more importantly, dispatch an approaching enemy soldier before he could discover the hiding Americans. Because of this secondary use, the Tunnel Weapon was returned to the manufacturer for improvements. Known by a new name, the QSPR or Quiet Special Purpose Revolver, only a few specimens of the improved weapon, and slightly over 600 rounds of improved ammunition, only a few grains lighter than the original round, were produced before the Vietnam War came to a close That officially ended the further development of the round and weapon. The primary improvements of the QSPR rounds was in the area of the primer to increase sensitivity to the firing pin impact.
