Colt CMG-2

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. The barrel had a 1:9 twist and was meant to fire an experimental 68-grain (4.4 g) bullet, designed for longer ranges than the then-standard 55-grain (3.6 g) M193 bullet. 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 handguard 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.

It was fed from a disintegrating metal belt using Stoner's proprietary S-63 BRW links. The S-63 BRW was a scaled-down 5.56mm NATO version of the M-60's M13 metal links for the 7.62mm NATO cartridge. Belted ammo was contained in a 150-round Stoner green or black plastic drum that mounted on the left-hand side of the weapon.

Colt submitted a buttstock-less short-barreled CMG-2 to the Navy SEALs. The Navy classified the CMG-2 as the EX 27 Mod 0 machine gun but they ultimately chose the Stoner 63 MK23 Mod 0 Commando instead. The CMG-2 never left the prototype phase and Colt ceased development in 1969.