The Winchester SPIW was an assault rifle designed for Project NIBLICK.
Winchester's design was rather innovative; it had a "short recoil" stock, where there was a spring in the stock. This supposedly allowed the rifle to dramatically increase accuracy when firing three round bursts, but it never really worked and the system was dropped. However, the grenade launcher component was found to be rather interesting and work continued on that portion. The system was later integrated with the Springfield design to little success.
The Winchester was a conventional rifle with a "short recoil" stock.
The rifle fired the 5.6×44mm XM144 flechette round.