The Colt Machine Gun or CMG was an open bolt belt-fed machine gun that fired 5.56×45mm cartridges designed by Colt Manufacturing Company in 1965. Colt hastily developed the CMG-1 to complement the CAR-15, a Colt branding of the M16 rifle, so that Colt might offer both of them as an alternative to the Stoner 63 weapons system. It failed to achieve any sales, and was replaced by the Colt CMG-2, which also failed to achieve any sales. The CMG-3 was a 7.62×51mm NATO version that failed as well.

In 1967, Colt replaced the CMG-1 with the CMG-2. The CMG-2 abandoned any commonality with the M16 and was only available as a bipod-mounted full-automatic-fire-only light machine gun with a vertical foregrip. The CMG-2 was gas-piston operated, but used a modified M16 bolt. The firing pin was double-sided, so it could be reversed if it was damaged or broken. The extractor was machined into the bolt and ejected spent rounds down through the vestigial magazine well. The fixed plastic stock was built into the back of the bolt-carrier group.

The CMG-2's barrel was detachable and had a folding handle, so an overheated barrel could be replaced in the field. Unlike the M60 machine gun then in use in the Vietnam War, which had its bipod and gas cylinder as integral to the spare barrel, an M2 bipod was mounted over the gas plug set in the CMG-2's ventilated hand-guard and was locked into place by the spare barrel's gas block.

The most unusual feature was that it lacked the charging handle of the M16. The operator charged the CMG-2 by unlocking the pistol grip and then sliding it forward and back to chamber a round from the belt and cock the weapon. A flat rectangular piece of metal slid on the trigger group's rails behind the trigger mechanism to act as a dust cover and keep debris out of the weapon.  (Wikipedia)

This 1970 proposal to the U.S. Air Force for the development of this machine gun followed the purchase of the AR-16 by the U.S. Air Force in 1962.  Colt already had a foot in the door with the AR-16 sale and expected a follow-up with this machine gun, but it was never adopted by the Military.

The photos showing the Colt history with machine gun development and the Colt factory Military Arms Division are historical on their own and shown below.