I remember seeing somewhere a light machinegun or automatic rifle in 5.56mm that used Ar-15/M-16 magazines, top-loading and bottom-ejecting like a Bren gun. I don't mean the Stoner rifle that could do that as one one of several possible configurations, I think this was something cheap meant as a low-cost guerilla weapon.
Does that ring a bell with anyone?
Does that ring a bell with anyone?