The Complete Guide to Colt M-16 Models: Part V

By Dan Shea

In this, the final part of our five part series on identifying the Colt Models, we touch on some very rare and interesting items. These were not “One offs”, but were never placed into full production. We have also added in the full list of what we know was manufactured by model number. If you have more information, please send it in, and SAR will publish an updated listing in about a year. Please watch for our upcoming ID Guides, where we cover the MAC models, the semi automatic AR 15 models by different manufacturers, the AK series, the FAL series, and the HK series as imported into the United States.

M-2 Beltfed M16

The Belt fed M16 was made on a heavy barreled Model 02, and was called the M2.

20 inch heavy barrel, 8.3 pounds without the bipod or ammunition box. There were heavy modifications to both the upper and lower receivers.

Many of the 120 round ammunition boxes have a link chute that returns the links to the box. This particular example does not.

Note the link chute space on the left of the lower receiver.

M16A2 Enhanced

20 inch heavy barrel, A2 buttstock, round forward assist.

The original “Flat-top” was on the “Enhanced” model, as seen here.

The fold down front sight was an attempt at both streamlining the rifle, and keeping it out of the way during scoped use.

M231 Firing Port Weapon

The Firing Port Weapon was made in the mid 1970’s for use in the ball mounting of a Bradley Fighting Vehicle. Around 27,000 were made. The high cyclic rate (1150 rpm) made these hard to control if dismounted, and most of the issue to the troops was made without the buttstocks. This open bolt FPW was full auto only.

ACR - Advanced Combat Rifle

Colt participated in the Advanced Combat Rifle trials, and their contender utilized an M16 lower receiver. Unlike some other ACR contestants, the Colt ACR used standard 5.56 ammunition.

The long heavy barrel sports an interesting flash hider / muzzle brake combination. Line of sight is augmented in the unusual buttstock, reminiscent of a vent rib on a shotgun. The collapsible stock is an enlarged version of the CAR stock, and has puzzled many people when seen without the gun.


The “Colt Machine Gun -1” was offered in 4 variations in their 1965 catalog, but never produced in more than a test run. Each prototype that was built was different internally. There was a tripod mounted version, a bipod mounted version, a tank version, and a solenoid operated version.

5.56 NATO caliber, weighing 12.5 pounds. Rate of fire was reported at 650 rpm.


In 1967 Colt fielded the CMG-2, an upgraded version of the CMG-1 design. This version cocked utilizing the pistol grip/ trigger group- pushing it forward and pulling the bolt to the rear. The extractor was machined into the bolt face. Colt used the 150 round drum to feed the linked ammunition.

If you are interested in a live fire test report, this author tested the CMG-2 for the “Battle of the Beltfeds” in Volume 10 Number 3 (September 1996) of Machine Gun News.


The “IMP” has had very little exposure. This bullpup pistol design was manufactured at Colt in the .221 Remington Fireball caliber, with its impressive ballistics. This revolutionary design allowed full auto fire from one hand, with a rifle cartridge. Bushmaster Firearms presented a copy of the IMP in its Bushmaster Pistol.

This article first appeared in Small Arms Review V1N9 (June 1998)
and was posted online on May 26, 2017


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