Colt US Property M231 Firing Port Weapon 5.56mm NATO Transferable Machine Gun


Status: In-Stock / Please Call to Purchase

This Chester County Armory listing is for an original Colt US Property marked M231 FPW (Firing Port Weapon) 5.56mm NATO transferable machine gun.

The M231 Firing Port Weapon was originally designed by Colt to attach and shoot from the firing ports on the M2 Bradley. This open-bolt redesign of the venerable M16 increases the firing rate of the weapon, dramatically, to approximately 1225 rounds per minute!

This model features original US Property markings on the left side of the receiver at the magazine well. In addition to the US Property marking, it also proudly displays the white Government Acceptance Stamp on the front of the magazine well.

In a unique twist on the M16 family, Colt’s manufacturing information is displayed on the right side of this weapon’s receiver, due to the design of the SAFE/AUTO fire controls on the M231, which has a metal plate that blocks the left side of the receiver where Colt typically marks other weapons in the M16 family. This M231 also features a unique (to the M16 family) barrel that measures 15.6″ in length.  The barrel is C MP CHROME BORE marked, as well.

This rarely seen M231 FPW also sports an even more rare, Colt factory-produced collapsible wire stock, which was originally created to allow the weapon to be deployed by a soldier outside of the M2 Bradley. Later versions of the M231 did not feature this ability, as after its adoption and use, the military decided that the wire stock wasn’t practical to maneuver inside an enclosed space when attached to the Bradley’s firing ports. The weapon features no sights, as it was originally intended to fire tracer rounds, so that the operator could see what they were aiming at through a window on the Bradley.

This unique machine gun is in excellent mechanical condition, and, based on the limited markings and wear noted on the internals, appears to have been fired very little, if it all. The internals show only minor markings on the face of the hammer. The bolt face is so clean and mark free, that this weapon appears to have been dry-fired more than any live firing, and may be unfired with live ammunition. The bore is extremely bright and shiny, with like-new depth and edging to the lands and grooves of the rifling.

Cosmetically, this weapon does note some minor handling marks in the exterior gray anodization, consistent with a military weapon of its age (see photos). However, it does not note any deep scratches, dings, dents, gouges, cracks, etc., or anything that would be problematic to its physical operation.

This US Property marked Colt M231 Firing Port Weapon chambered in 5.56mm NATO is a fully transferable machine gun, and it is currently on a Form 3 for easy transfer.

We also currently have a large inventory of replacement parts for the M231 available, including bolts, springs, fire control groups, gas seals, etc. We will include a small assortment of replacement parts and springs with the purchase of this machine gun.

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    5.56mm NATO


    Gas Operated, Open Rotating Bolt

    Barrel Length



    7.34 lbs


    Colt Anodized Gray