sd_matt: I’m going to date myself a little bit here, but we used to have a variant of the M-60, the A3, that featured a shorter barrel and a foregrip. That weapon was a real chopper, and was chambered for 7.62mm.
I carried a CAR-15 for a bit and liked the weapon, especially it’s size and weight, but disliked the 5.56mm round.
Completely off the machine gun topic, have you seen the AA12? Fully automatic 12ga.