digplanet beta 1: Athena
Share digplanet:


Applied sciences






















Submachine Gun, 5.56mm: Port, Firing, M231
Type Firing Port Weapon/Assault rifle
Place of origin  United States
Service history
In service 1980–present
Used by United States of America
Wars Gulf War, Iraq War
Production history
Designed 1979
Produced 1980-present
Variants None

Empty - 7.34 lb (3.33 kg)

w/ 30 round magazine - 8.34 lb (3.79 kg)
Length 28.25 in. (71.76 cm)
Barrel length 396 mm (15.6 in)

Cartridge 5.56×45mm NATO
Action Gas-operated, rotating bolt
Rate of fire

Sustained (Short Bursts) - 50–60 rounds per minute

Minimum Cyclic - 1225 rds per min
Effective firing range 328 yds (300 m)
Feed system 30-round STANAG Magazine

The M231 Firing Port Weapon (FPW) is an adapted version of the M16 assault rifle for firing from ports on the M2/M3 Bradley AFV. The infantry's normal M16s are too long for use in a "buttoned up" APC, so the FPW was developed to provide a suitable weapon for this role. Designed by the Rock Island Arsenal, the M231 FPW remains in service, although all but the rear two firing ports on the Bradley have been removed.


Work started in 1972 on a dedicated Firing Port Weapon to go along with the Mechanized Infantry Combat Vehicle (MICV) program also started at that time. A requirement for these vehicles was to have firing ports for troops riding inside, and so it was decided that a specific weapon also be developed. The Rock Island Arsenal headed up the project working with the M3 sub-machine gun, an FPW created by HK based around the HK33, and a modified AR-15/M16 pattern weapon. The qualities of the last weapon made it most promising, and by 1974 it had been designated XM231. Colt was given the contract and continued to work on the design, and by 1979 the finalized weapon was adopted as the M231.

Although most of the Bradley AFV's ports have since been removed, these weapons are maintained, and are used by crews for self-defense, close-quarters situations, and for firing from the rear door firing ports as intended.


M231 FPW

The M231 is different in many ways from a standard M16. The original RIA FPW fired from an open bolt, with an extremely high rate of firing (1,050 rpm). The Colt XM231 introduced a special buffer and spring assembly, with three springs nested one within the other. This was done to allow the rate of fire to be lowered to 200 rpm, because the theory at that period was that, while using all tracer bullets in the magazine, if the high rate of fire (ROF) was retained troops would exhaust their magazines before the weapon was brought to target. The original RIA FPW had an 11 inch (280 mm) barrel, while the Colt prototypes and the production M231 both had 15.6 inch (396 mm) barrels. Initially the FPWs had no locking mechanism and had flip up sights, along with a metal wire stock akin to that on the M3 sub-machine gun, to allow the weapon to be used outside of the vehicle more effectively. Later this was dropped, and a new hand-guard introduced with a screw type locking mechanism to fix the weapon into the port. Late XM231s had no rear sights either. By the time the M231 was finalized the wire stock had been done away with as the weapon had a tendency to unfasten itself from the firing port and the stock was deemed to be dangerous in the confines of the vehicle (or, alternately, Army officials omitted the feature to discourage troops from employing the M231 in lieu of the issue M16 rifles). The firing rate had also returned to a higher rate of 1,100-1,200 round/min.

These weapons are only capable of fully automatic fire, with a special side plate mounted inside the lower receiver and a selector that only has "safe" and "auto" positions.[1] These weapons retain a 65% commonality with standard M16 rifles. Only the M196 tracer round was authorized for operational use, with the M199 dummy and M200 blank for training use. In an emergency M193 ball ammunition was to be used. The heavier M855 ball and M856 tracer rounds were never to be used.[2]

Officially the FPW was not to be used detached from the parent vehicle, unless in an emergency. The operator's manual pointed out 4 precautions that would have to be taken to utilize the weapon not attached the vehicle. These included a note about the excessive muzzle rise of the weapon during firing, that the barrel collar would become hot when firing and should not be touched, that hearing protection should be worn, and lastly that a brass catching bag or evacuation hose system would have to be installed.[3]



  1. ^ http://www.ak47.net/forums/t_3_123/459672_index.html/page=1
  2. ^ United States, 1997. p. 4-2
  3. ^ United States, 1997. p. 1-1-2


  • Long, Duncan. The Complete AR-15/M16 Source-book. Boulder, CO: Paladin Press, 2001. ISBN 0-87364-687-8.
  • United States, Headquarters, Department of the Army. TM 9-1005-309-10, Operator's Manual, Sub-machine Gun, 5.56mm: Port, Firing, M231. Washington, DC: Headquarters, Department of the Army, 1997.

See also[edit]

Original courtesy of Wikipedia: http://en.wikipedia.org/wiki/M231_Firing_Port_Weapon — Please support Wikipedia.
A portion of the proceeds from advertising on Digplanet goes to supporting Wikipedia.
13 videos foundNext > 

!!KICK ASS!! US Army Bradley Fighting Vehicle !!MUST SEE!!

NOW HIRING BRADLEY MECHANICS!! Join the California Army National Guard and serve 1 weekend per month and 2 weeks during the summer maintaining Bradley Figh...

M16 M231 prototype full auto test

Replica of the M231 firing port weapon stock, made for use with standard ar15 or m16 rifles. Unlke the original this one is closed bolt and works with a stan...

Arma2: M231 FPW W.I.P

Quick demo of the M231 Firing Port Weapon after adjusting the ROF and recoil values.

automatic m4

m-231 port firing weapon.


me shooting a sweet ass port gun ( AKA M231), 30 rounds 5.56 in under 2 sec.

Armor and Impoverished Opposition

M231 Firing Port Weapon was for the M2/M3 Bradley only*** Irish's S-4 http://astore.amazon.com/irss4-20.

Special Firearms

Song "America - Beautiful Home Before Change" by Rafael Brom on iTunes https://itunes.apple.com/us/album/change/id284435397 Cosmotone Records / Cosmotone Mus...

5.56mm FPW Bradley CLAW turret & M113 Gavins dynmicpara

With their side firing ports covered over with extra armor, thousands of full-auto M231 5.56mm firing port weapons (FPWs) are sitting unused in arms rooms ac...

The REAL Bradley "Fighting" Vehicle! Chapter 16: More Fun Facts (Part 5/10)

The halfway point of this chapter contains a smorgasbord of less-celebrated facts about the Bradley, spread over a wide range of issues. These include --- bu...

The 40mm Machine Gun

FPSRussia Shirts My Twitter: My Facebook: Business Email: THEFPSSHOW@Gmail.com Pre 68 amnesty registered breach ring. Civilian legal full auto artillery piec...

13 videos foundNext > 

We're sorry, but there's no news about "M231 Firing Port Weapon" right now.


Oops, we seem to be having trouble contacting Twitter

Talk About M231 Firing Port Weapon

You can talk about M231 Firing Port Weapon with people all over the world in our discussions.

Support Wikipedia

A portion of the proceeds from advertising on Digplanet goes to supporting Wikipedia. Please add your support for Wikipedia!