M240 7.62mm Armor Machine Gun
Gary's Combat Vehicle Reference Guide

Alternative DesignationsM240 Fixed Machine Gun, M240 Tank Machine Gun
Country of OriginBelgium
Caliber0.3 in (7.62 mm)
Cartridge7.62 mm NATO


The U.S. Army adopted the Belgian Fabrique National MAG (Mitrailleuse d'Appui Générale, or Mitrailleuse à Gaz) medium machine gun as the M240 in 1977 to replace the M73/M219 7.62mm and M85 .50 caliber tank machine guns.

The M240 7.62mm machine gun is used to engage enemy personnel, infantry crew-served weapons, anti-tank guided missile teams, and unarmored vehicles. The M240 is a belt-fed, air-cooled, gas-operated, fully automatic weapon with a maximum effective range of 900 meters (tracer burnout). The bore of the barrel is chromium plated, reducing barrel wear to a minimum.

The M240 is part of the secondary armament on the U.S. Army M1 series Abrams tank, M2/M3 series Bradley Fighting Vehicle, and the U.S. Marine Corp LAV-25.


MAG 58 Coaxial
The MAG 58 out-performed all competitors in testing to select a better coaxially-mounted weapon for U.S. tanks. Reliability and maintainability were the weapons advantages of this weapon, as well as lower life cycle costs.
Coaxially mounted version.
Pintle-mounted version.
U.S. Army ground (infantry) version of the M240/M240E1. Replaces the M60 series machine guns.
U.S. Marine Corps ground version of the M240/M240E1. Replaces the M60E3 machine gun.
Aviation variant which will replace the M60D. The M240E5 will use the same receiver and barrel as the M240B but will have a spade grip trigger assembly. It will also require a unique mounting interface and pintle to properly interface with the helicopter platform. Also included with the system will be an egress kit to allow the weapon to be converted for a grounds defensive role in the event the helicopter is downed.


FM 3-22.68: 7.62mm belt
Ammunition is fed into the weapon using a disintegrating metallic split-link belt. The gas from firing one round provides the energy for firing the next round. Thus, the gun functions automatically as long as it is supplied with ammunition and the trigger is held to the rear. As the gun is fired, the belt links separate and are ejected from the side. Empty cases are ejected from the bottom of the gun.

The M240 machine gun has three rates of fire: cyclic, sustained, and rapid.
  1. Cyclic Rate. At this rate, the gun fires 100 rounds a minute, with 4 to 5 seconds between each burst. The gunner must change the barrel every 10 minute
  2. Sustained Rate. The gunner can shoot 100 rounds a minute, plus or minus 25 rounds.
  3. Rapid Rate. At this rate, the gun fires 200 rounds a minute, with 2 to 3 seconds between each burst. The gunner, must change the barrel every 2 minutes.

Cycle of functioning (many of the actions occur at the same time and are separated only for teaching purposes).

The cycle starts when the first round of the belt is placed in the tray groove. Then the trigger is pulled, releasing the sear from the sear notch. When the trigger is pulled to the rear, the rear of the sear lowers and disengages from the sear notch. This allows the bolt and operating rod assembly to be driven forward by the expansion of the driving spring rod assembly. The cycle stops when the trigger is released and the sear again engages the sear notch on the bolt and operating rod assembly.
  1. Feeding. The actuating roller moves the feed lever side to side, which in turn moves the feed pawls. The forward movement of the bolt forces the outer pawls to the right, fully feeding the round. The inner pawl rides over the round and settles behind it. The rearward movement forces the inner pawl to the right, fully feeding the round. The action of fully feeding a round pushes the link of a fired round out of the side of the gun. The last link in a belt cannot be pushed out and is cleared during the unloading.

  2. Chambering. The first round is positioned in line with the chamber and is held in position by the cartridge stop and cartridge guide pawl. On trigger squeeze, the nose of the sear is depressed thus freeing the piston rod extension. The driving spring rod assembly pushes the working parts forward. The feed horn strikes the base of the round. The bolt strips the round from the belt link. The chambering ramp angles downward and, along with the spring tension of the cartridge guide pawl, forces the round toward the chamber. The cartridge guide pawl also holds back the belt link. When the round is fully seated in the chamber, the extractor snaps over the extractor rim of the cartridge, and the ejector is depressed.

  3. Locking. During chambering, as soon as the piston begins to move, the firing pin is withdrawn into the bolt block. The breech remains locked during the primary movement. The bolt enters the barrel breech as the operating rod is driven forward by the drive spring, and as the locking lever, which the bolt is riding on, swings forward, pushing the bolt forward and locking it to the barrel breech. Although the term "locking" is used here, in the M240, the bolt and barrel do not physically interlock. This way, the barrel can be removed when the bolt is forward.

  4. Firing. As the working parts come forward and the round is fed into the chamber, the locking lever is forced down by the locking cams. This slows down the forward movement of the bolt assembly. The piston rod extension, still moving forward, causes the locking lever link to rotate downward and back. This forces the arms down to their fullest extent in front of the locking shoulder. The extractor rises over the base of the round and the ejector is compressed. The round is now fully home with the breech locked. The final forward movement of the piston extension drives the firing pin through the bolt assembly onto the cartridge primer and fires the round. The working parts are now fully forward.

  5. Unlocking. When the round is fired, some of the gases pass through the gas plug regulator into the gas cylinder. The rapidly expanding gases enter the hollow end cap of the gas piston and force the operating assembly to the rear. This powers the last four steps in the cycle of functioning. During the primary movement of the operating rod assembly, it moves independently of the bolt for a short distance. At this point, the locking lever begins to swing toward the rear, carrying the bolt with it into its unlocked position, and clearing the barrel breech. When the bolt assembly has been jerked back, slightly enough to unlock the breech, the primary effort is extraction of the empty case.

  6. Extraction. When the breech is fully unlocked and the bolt assembly starts its rearward movement, the extractor withdraws the empty case from the chamber.

  7. Ejecting. As the cartridge case is withdrawn from the chamber, the ejector pushes from the top, and the extractor pulls from the bottom. The casing falls down from the face of the bolt as soon as it reaches the cartridge-ejection port. The empty belt links are forced out the link ejection port as the rearward movement of the bolt causes the next round to be positioned in the tray groove.

  8. Cocking. As the working parts continue toward the rear, the return spring is compressed; the trigger is kept squeezed; sufficient is gas made available by the gas-regulator adjustment, which causes the working parts to rebound off the buffer; and the action of feeding and firing continues. In releasing the trigger, the sear remains down, but the tripping lever rises. As the working parts come to the rear, the end of the piston rod extension hits the tripping lever, which, in turn, allows the sear to rise and engage the sear notch, which holds the working parts to the rear.


Ammunition is issued in a disintegrating metallic split-linked belt (M13 links). The preferred ammunition mix for the M240 is four ball and one tracer. Other types of 7.62mm ammunition are available. However, the four-and-one mix allows the gunner to use the tracer-on-target (TOT) method of adjusting fire to achieve target kill or suppression. Click here for more information about 7.62mm ammunition.