Special Purpose Individual Weapon [SPIW]
A completely new kind of weapon called SPIW (Special Purpose Individual Weapon) was in the process of development in the 1960s. The new SPIW was to combine the capabilities of a rifle, a controlled pattern shotgun, and a light mortar. It could be designed to fire a single medium-sized dart, a cluster of small darts, a microcaliber bullet, or a high explosive round. Many military experts predicted that the SPIW, or something like it, would become the basic infantry weapon of the future. By the end of 1969, however, the SPIW was still purely experimental, and no such weapon was available to the infantryman fighting in Vietnam.
The Special Purpose Individual Weapon was mainly focused on developing a flechette-firing rifle. The Special Purpose Individual Weapon was to be a hand held weapon holding 60 rounds of point target ammunition, deliverable in the form of controlled bursts of tiny, lethal darts or "flechettes".
In 1966, engineers working at AAI Corporation, one of the companies involved in the project, filed applications for patents on a "concave-compound finned projectile" and a "multiple hardness pointed finned projectile" (granted as US patent numbers 3,861,314 and 3,851,590 respectively). The purpose of both of these constructions was to make the nose deform on impact, causing the flechette to tumble. ("It will be readily apparent that increased effectiveness is obtained with this projectile in a soft, dense type target, such as an animal, due to the tumbling and enlarged effective projected peripheral area of the projectile in the tumbling curled configuration . . . as compared to the small piercing configuration of the projectile if it should pass into or through the target in a straight linear fashion", the inventor wrote in the second patent application cited above. The first application contained similar language.)
Another design, tested for wounding effects at the US Army Ballistic Research Laboratories, was for a bimetallic flechette; the two metals would have separated on impact, greatly increasing the area pushing against the flesh. The deformation of the first two flechettes is very close to the "expanding" or "flattening" of dumdum bullets, in the terminology of the Hague Declaration, and the break-up of the bimetallic flechette would be prohibited under the Hague Declaration if the Declaration were applied to flechettes.
It is known to surround an undersized rifle projectile with a plastic cup (sabot) which is engraved and spun by the barrel rifling and which in turn transmits the spin to the projectile by virtue of a tight friction grip. This has the disadvantage that the sabot material must have a high coefficient of friction to maintain its grip on the projectile, with a correspondingly high friction loss in the barrel. A further consequence is that the combined mass of the sabot and projectile is less than that of a conventional projectile of the same size, which therefore has less impulse for the same energy. The advantage of this is less gun recoil, but the disadvantage is that an unmodified conventional cartridge gun, will not complete its automatic cycle because of the reduced impulse.
It is also known to use a plastic sabot to surround a flechette and to have the barrel rifling only engrave the sabot, which transfers the rotation to the flechette by mechanical engagement with the fins of the flechette, instead of by a friction grip, and therefore a low coefficient of friction material can be used for the sabot with a resulting low friction loss in the barrel. One consequence of using a flechette however is that the combined weight of the sabot and flechette is very light when compared to a conventional bullet of the same diameter and length so that a special automatic gun must be used to function with the reduced impulse. A further problem with all sabot launched projectiles is that since the sabot and projectile exit from the barrel at the same velocity, the energy of each is determined by their relative mass to one another. The heavier the sabot is in relation to the projectile, the greater is the percentage of lost energy, since the sabot serves no useful purpose as a projectile. In the prior art, the body diameter (shaft) of a flechette is small in comparison to the sabot diameter, with a resulting large proportion of mass and energy in the sabot, so that the flechette gets a relatively small amount of the total energy and is therefore the least efficient of the sabot type projectiles.
The SPIW was both a "point fire" weapon that shot bursts of 13-grain flechette projectiles, and an "area fire" weapon that shot 40mm grenades -- ala the M-79. The SPIW went through at least three generations before it became the SBR -- Serial Bullet Rifle -- and then faded away in the mid-1970s.
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