Special Purpose Individual Weapon - Project NIBLICK

Meanwhile the Army's Operations Research Office, ORO, had been working on Project NIBLICK, follow-on to SALVO to develop a modern grenade launcher. Interested in the original shotgun-type shells, they recommended development of a dedicated flechette-firing weapon combined with a grenade launcher, the SPIW. The final requirements resulted in an over-under weapon, firing flechettes from one barrel, and grenades from the other. It was to weigh under 10 pounds (4.5 kilograms) fully loaded with three grenades and 60 flechettes.

Four companies responded to the contract tender: AAI, Springfield Armory, Winchester Arms and Harrington & Richardson. AAI continued with the original 5.6x53 mm XM110 rounds, while Springfield and Winchester used a new 5.6×44 mm XM144 cartridge. The H&R design loaded the dart from the XM144 into their own cartridge design.

The H&R design was the most advanced. It mounted the dart between three plastic sabots in a triangular plastic cartridge. When fired, the sabots were discarded early in small "sub-barrels" while the dart continued down the main barrel. Although the rounds were lightweight the weapon itself was not, at 24 pounds (11 kilograms) loaded, and the weapon was quickly eliminated from the contest.

Winchester's design used a "soft recoil" stock which absorbed the recoil of an individual round in a spring. The idea was to allow three rounds to be fired before the spring was completely compressed, meaning that there was very little recoil until the end of the burst. This was intended to dramatically increase the accuracy of burst fire, but the system never truly worked, and was later dropped. The grenade launcher portion of the design proved much more interesting, however, and work continued on that portion.

The Springfield entry was most interesting for its layout. It used two 30-round magazines back-to-back in a bullpup layout, taking rounds from the front magazine first. However, their massive magazine-fed grenade launcher pushed the weight to 14 pounds (6.4 kilograms), and it seemed unlikely this could be reduced by much.

Oddly, AAI's design was the least technically advanced. The flechette gun portion was somewhat heavy, but fired at 2400 rpm. Their grenade launcher was a simple single-shot weapon; their semi-automatic version was not ready in time for testing.

The conclusion of the testing was that none of the weapons were ready for development into a combat system. The AAI flechette portion and the Winchester grenade launcher were both interesting for general development, however. More worrying was the result of general testing of the flechette concept. While the weapons delivered on their promise of extremely high rates of fire and excellent penetration, the rounds themselves were extremely expensive to produce, and the darts could be easily deflected in flight even by heavy rain. Finally, the rounds gave off extremely loud reports and had a huge muzzle flash, making the guns easily visible in low light.

A second round of testing followed, with the Springfield model adopting the Winchester grenade launcher with a disposable magazine and a new side-by-side layout for the flechette magazines. AAI's design was equipped with their semi-automatic launcher, which was now complete, and a new plastic buttstock/sighting system. Neither updated version proved very reliable and both were over the 10 pounds (4.5 kilograms) limit. In 1966 SPIW was put into "maintenance mode" and the M16 adopted.

AAI continued development at a low level, and eventually managed to dramatically improve the reliability of their XM19. However, this revealed another problem: heat buildup in the chamber was great enough to result in "cook off". Changes in the Army command structure and the adoption of the M16 made interest in the SPIW fade, and eventually the project was allowed to die. Ironically, AAI's original "simple" grenade launcher turned out to be a major success: it was selected as the M203 in 1968 and became a common weapon under the M16.