SPIW
| Special Purpose Individual Weapon | |
|---|---|
|
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| Type | Bullpup flechette rifle |
| Place of origin | United States |
| Production history | |
| Designed | 1951 |
| Specifications | |
| Weight | 3.5 lb (1.6 kg) (Project SALVO) 10 lb (4.5 kg) 24 lb (11 kg) 14 lb (6.4 kg) (Project NIBLICK) |
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| Cartridge | 12 gauge flechette rounds, XM110 5.6×53mm (Project SALVO) |
| Rate of fire | 2300 rpm (Project SALVO) 2400 rpm (Project NIBLICK) |
| Feed system | 60-round detachable box magazine (Project SALVO and NIBLICK) |
| Sights | None |
The Special Purpose Individual Weapon (SPIW) was a long-running United States Army program to develop, in part, a workable flechette-firing "rifle", though other concepts were also involved. The concepts continued to be tested under the Future Rifle Program and again in the 1980s under the Advanced Combat Rifle program, but neither program resulted in a system useful enough to warrant replacing the current M16.
The idea of a flechette-firing individual weapon started in earnest during the Army's Project SALVO. SALVO had earlier concluded that a small weapon with a high rate of fire would be considerably deadlier than the large "full power" weapons being developed in the 1950s, and followed several lines of investigation to find the best way to provide high firing rates. SALVO had a small number of "duplex load" weapons developed, where two bullets were stacked, while Springfield Armory and Olin/Winchester both entered multiple barrel firearms.
Even before the SALVO tests, Irwin Barr of AAI Corporation had been developing single and multiple flechette cartridges. The Navy became sufficiently interested in the concept to provide him with some development funding from the Office of Naval Research, resulting in a 12 gauge shotgun shell firing 32 flechettes. The Army later added funding as well, and AAI was invited to SALVO. In SALVO testing they were found to be able to penetrate one side of a standard steel helmet at 500 yards (460 m)—excellent given their light weight—but the dispersion of the darts was so great as to make them only marginally useful.
Further development continued by adapting a Winchester Model 70 rifle with new XM110 5.6×53 mm rounds firing a single dart. The result was a weapon with somewhat less accuracy than the 7.62×51mm NATO rounds, but with equal penetration and a trajectory so flat it could be fired with no sight adjustment out to 400 yards (370 m). Better yet the rounds were very light, and had almost no recoil in comparison to even the 0.22-inch caliber weapons under development. This meant they could be fired at extremely high rates of fire, from a very lightweight weapon.
Project SALVO began in 1951 and was based on the assumption that firing multiple projectiles would increase the probability of hitting the target. During World War II, an infantryman with a rifle at an average engagement distance of 300 yards under combat stress expended 10,000 rounds for one hit. Consideration to lighter ammunition types and rifle/grenade launcher combinations was given. Flechettes were found to be inaccurate and expelled fiberglass fragments with each round fired. SALVO mainly studied weapons and ammunition as opposed to developing them. It determined that higher velocity projectiles, smaller than 7.62 mm, had equal or greater lethality with less weight. It also found that fully automatic fire did not increase hit probability.
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