The SPIW program began in 1962 with entries from Colt, Springfield, AAI, and Winchester. The first set of trials were a complete failure, and both Colt and Winchester abandoned the project at that point. AAI pressed on, producing these second generation rifles – one for trials in 1966 and one after. Both are chambered for the XM-645 5.6x57mm single-flechette cartridge. Under testing, both showed multiple serious problems in reliability, noise, cook-offs, and accuracy. The company would struggle on for years continuing to develop the flechette rifle system, but would be ultimately unsuccessful.
Thanks to the Rock Island Arsenal Museum for allowing me access to film this very interesting rifle! If you are in the Quad Cities in Illinois or Iowa, the Museum is definitely worth a visit. They have a great number of small arms on display as well as an excellent history of the Rock Island Arsenal.