This belt-fed iteration of the M-16 was basically an experimental firearm. Only 20 of these guns were ever made before the project was canceled. Chambered in 5.56x45mm, this machine gun has a 21-3/4″ heavy profile barrel with a bipod attached right behind the three-prong flash hider. Here is how Morphy Auction describes the feeding mechanism of this gun:
Colt then added a very clever belt feed mechanism, that sits in the magazine well when the rifle is opened and locks in when the rifle is closed. The vertical actuator attaches to a special cut in the bolt carrier group to actuate, and a slot was added on the right side, where a feed chute would feed spent links into a separate compartment of the feed box.