The Colt Machine Gun or CMG was an

open bolt A firearm is said to fire from an open bolt or open breech if, when ready to fire, the bolt and working parts are held to the rear of the receiver, with no round in the chamber. When the trigger is actuated, the bolt travels forward, feeds a car ...

belt-fed machine gun that fires 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 The M16 (officially Rifle, Caliber 5.56 mm, M16) is a family of assault rifles adapted from the ArmaLite AR-15 rifle for the United States Armed Forces, United States military. The original M16 was a 5.56×45mm NATO, 5.56×45mm automatic ...

, 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 The 7.62×51mm NATO (official NATO nomenclature 7.62 NATO) is a rimless, straight walled, bottlenecked, centerfire rifle cartridge. It is a standard for small arms among NATO countries. First developed in the 1950s, the cartridge had first be ...

version that failed as well.

Colt Machine Gun #1 (CMG-1)

Though marketed together with the CAR-15, the CMG-1 had few parts in common with it. One CMG-1 used

direct impingement Direct impingement is a type of gas operation for a firearm that utilizes gas from a fired cartridge to impart force on the bolt carrier or slide assembly to cycle the action. Firearms using direct impingement are theoretically lighter, more acc ...

and shared the bolt, gas tube, and other operating parts of the M16. However, other CMG-1s used gas pistons. The CMG-1s also used the M16's

pistol grip On a firearm or other tools, a pistol grip is a distinctly protruded handle underneath the main mechanism, to be held by the user's hand at a more vertical (and thus more ergonomic) angle, similar to how one would hold a conventional pistol. ...

, front sight block, and flash hider. Similar to the Stoner 63, the CMG-1 could be fed from either side. The rate of fire was 650 rounds per minute. Only two or three CMG-1s were ever made. Colt made them with sheet-metal stamping. Colt offered the CMG-1 in four different versions: bipod-mounted, tripod-mounted, vehicle-mounted, or fixed mount. The . bipod-mounted version was marketed as a light machine gun for use by assault troops. It was the only version with a buttstock. The . tripod-mounted version was considered a medium machine gun. The vehicle mounted version was a pintle-mounted machine gun for use by soldiers in land vehicles. The fixed mount version was fired by a

solenoid upright=1.20, An illustration of a solenoid upright=1.20, Magnetic field created by a seven-loop solenoid (cross-sectional view) described using field lines A solenoid () is a type of electromagnet formed by a helix, helical coil of wire whos ...

allowing for remote operation so it could be mounted in a helicopter or other aircraft.

Colt Machine Gun #2 (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 bullet, designed for longer ranges than the then-standard M193 bullet. Unlike the

M60 machine gun The M60, officially the Machine Gun, Caliber 7.62 mm, M60, is a family of American general-purpose machine guns firing 7.62×51mm NATO Cartridge (firearms), cartridges from a disintegrating Belt (firearms), belt of M13 links. There are sev ...

then in use in the

Vietnam War The Vietnam War (1 November 1955 – 30 April 1975) was an armed conflict in Vietnam, Laos, and Cambodia fought between North Vietnam (Democratic Republic of Vietnam) and South Vietnam (Republic of Vietnam) and their allies. North Vietnam w ...

, 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 The drum is a member of the percussion group of musical instruments. In the Hornbostel–Sachs classification system, it is a membranophone. Drums consist of at least one membrane, called a drumhead or drum skin, that is stretched over a ...

that mounted on the left-hand side of the weapon. Colt submitted a buttstock-less short-barreled CMG-2 to the

Navy SEALs The United States Navy Sea, Air, and Land (SEAL) Teams, commonly known as Navy SEALs, are the United States Navy's primary special operations force and a component of the United States Naval Special Warfare Command. Among the SEALs' main funct ...

. 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.

Colt Machine Gun #3 (CMG-3)

A version chambered in 7.62 mm was made in the early 1970s. Only a limited number were manufactured, estimated to be around 5, with 2 remaining in existence.

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