Colt ACR Advanced Combat Rifle M16A2 5.56mm Duplex Transferable Machine Gun w/ Experimental Serial Number


Status: In-Stock / Please Call to Purchase

This Chester County Armory listing is for a rare, factory original Colt M16A2 ACR Advanced Combat Rifle 5.56mm NATO Duplex fully transferable machine gun.

This amazingly rare specimen is one of only a very few, fully transferable ACR’s on the NFA registry, making it a highly sought-after prize by Colt and M16 collectors. Originally designed by Colt in 1982 and submitted to the US Military for consideration in the Advanced Combat Rifle program, this unique variant of the M16 allowed for the firing of specialized 5.56mm duplex rounds, created by the Olin Corporation for this specific weapon. 

This new ammunition was basically a standard 5.56mm NATO cased cartridge that held two separate bullets, designed to make every round fired a double-tap. The concept was to get more projectiles downrange for every shot fired, so as to increase battlefield casualties, especially at closer ranges.  The ACR can also be used to fire standard 5.56mm NATO rounds, as well, with no changes other than the swapping of the ammunition.  For long range engagements (further than 325m), a soldier would simply change mags, discharging the duplex rounds for a new magazine loaded with standard 5.56mm NATO single projectile loads to increase accuracy at further distances. 

While the weapon system performed excellent in military field trials, the US Military eventually shelved the program, noting not enough improvement over the venerable M16 to justify the cost of implementing the new platform.

This unique, transferable machine gun is ACR roll marked with an X marked serial number from Colt (X27754), designating it as a Colt experimental version. This model features the original design ACR pistol grip and handguard (including the white, quick acquisition stripe on the top of the handguard), as well as an eight-position collapsible butt stock design. This particular model also features a rare, flip-up sight that was built into the upper receiver and housed underneath a removable carry handle. The carry handle for this version of the ACR was designed by Colt as being more compatible to a standard M16A2, to allow them to be interchanged between the weapons, instead of the ACR specific forward slanted model.

This machine gun is in excellent overall condition.  While many X marked Colt prototypes often have seen significant firing use, that does not appear to be the case with this model. This model appears to have been fired very little, if at all. Mechanically, the internals are in beautiful condition, with only minor markings noted. The bore is bright and shiny with crisp rifling. The BCG group does not note any wear, nor does the upper receiver. Any markings on the gun appear to be only cosmetic in nature in the exterior parkerization.  There is a slash mark that appears over the ACR logo. This mark is only cosmetic and is not deep. This mark occurred while the weapon was still in Colt’s possession. The weapon notes no dings, dents, gouges, cracks, etc., or any type of concern that would cause a problem with operation of the weapon. 

The Colt ACR uses a lower that is dimensionally identical to a standard M16 lower, the only difference discerned is the original ACR markings.  Any standard pin M16 upper will also work on this lower. The fire controls and bolt carrier group are also standard M16 items.  The difference in the ACR comes in the barrel and upper receiver designs.

As the Colt ACR has the ability to fire both standard 5.56mm NATO rounds (as well as the specifically-designed 5.56mm duplex rounds); the listed price for this item will also include 10 boxes (200 rounds) of original, factory, Olin manufactured duplex ammunition that was created specifically for the Colt ACR.

This historical and rare collectible machine gun is fully transferable. It is currently on a Form 3 for easy transfer.


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    This Chester County Armory sale listing is for a rare, factory original Colt M16A2 ACR Advanced Combat Rifle built to fire the 5.56mm duplex rounds. This original and rare machine gun is fully transferable. This model is currently in-stock, in our possession,  and available for purchase on a Form 3. Please call us at 610-235-6155 to purchase or for additional information on this item.




    ACR / M16A2


    5.56mm NATO


    Gas Operated, Rotating Bolt

    Barrel Length



    Colt Anodized Gray