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Today we are looking at the Winchester company's entry into the 1964 SPIW (Special Purpose Infantry Weapon) trials. The SPIW program was an attempt to increase small arms lethality by increasing hit probability with ideas like hyper-velocity flechette cartridges and burst fire trigger mechanisms. In addition, the weapons were required to incorporate area-effect elements - aka grenade launchers.

This design used a 60-round drum magazine firing a high velocity flechette as well as having a blow-forward semiautomatic 40mm grenade launcher attached to the muzzle. One of the biggest challenges in the development was the flechette cartridge itself - the sabot holding the dart in place had to be loose enough to cleanly detach at the muzzle, but also tight enough to pull the dart down the barrel.

Ultimately, none of the 1964 trials weapons were successful, and this Winchester design was particularly…