page_title: M240 machine gun
section_title: Operation
hierarchical_section_title: M240 machine gun / Operation
caption_attribution_description: English: Members of an M1 Abrams main battle tank crew man the tank commander's M2.50-caliber machine gun, left, and the ammunition loader's M240 7.62 mm machine gun. Released to Public Date Shot: 1 Jun 1981
context_page_description: The M240, officially the Machine Gun, 7.62 mm, M240 or unofficially the M240 Bravo, is the US military designation for the FN MAG, a family of belt-fed, gas-operated medium machine guns that chamber the 7.62×51mm NATO cartridge.
  The M240 has been used by the United States Armed Forces since the late 1970s. It is used extensively by infantry, most often in rifle companies, as well as on ground vehicles, watercraft and aircraft. Despite being heavier than some comparable weapons, it is highly regarded for reliability and its standardization among NATO members is a major advantage.
  All variants are fed from disintegrating belts and are capable of firing most types of 7.62 mm NATO ammunition. M240 variants can be converted to use non-disintegrating belts. There are significant differences in weight and some features among some versions which restrict interchangeability of parts. The M240s used by the US military are currently manufactured by FN America, the American subsidiary of FN Herstal.
  The M240B and M240G are usually fired from integrated bipods, tripods, or vehicular mounts; regarding tripod use, the U.S. Army primarily uses the M192 lightweight ground mount, while the U.S.
context_section_description: Loading the M240 can be done either with the bolt forward or to the rear. If the bolt is to remain forward, the operator will then load the rounds into the feeding block (feed tray cover closed); or will open the feed tray cover, load the rounds onto the feeding tray, then close the feed tray cover. The charging handle will then be pulled to the rear, which locks the bolt to the rear. The weapon is then placed on safe and the charging handle is then placed back to the forward position (this is spring-loaded on the tank-mounted variation). The weapon is now ready for operation.
  
  The weapon fires from the open bolt position, meaning that the bolt is held to the rear and only moves forward as it is firing a round. The firing pin is static and the bolt moves around the firing pin, circumventing any need for a hammer. A sear is used to time the internal mechanisms of the weapon to provide a consistent rate of fire, ensuring proper function and accuracy. However, firing from an open bolt also provides the possibility of an accidental discharge due to a bolt override. This happens when there is enough force for the bolt to jump over the sear and fire without the trigger being pulled. The safety on the weapon cannot stop this from happening. The safest way to protect against this is to leave the bolt forward on the weapon until the operator is ready to fire the weapon; then charge the weapon and fire.
  Clearing the weapon is performed by ensuring that the bolt is locked to the rear and the weapon is on safe. The top cover is then lifted, the remaining belt (if any) is swept out of the feed tray, the feed tray is lifted to visually inspect the chamber and the face of the bolt. Any links or brass casings are removed. The weapon is now clear. In the extremely unlikely event that a live round is on the bolt face, it is knocked loose with a cleaning rod or another rigid object. If there is a live round lodged in the barrel, the operator must immediately decide if the barrel is hot enough that there is a chance of it cooking off. If there is, they will immediately move their face away from the opening of the weapon; and aiming the gun in a direction that is perceived to take the least amount of damage or casualties should the event of a cook-off occur. They will then wait for the barrel to cool off before attempting to remove it. They can also attempt to extract the round by closing the cover, taking the weapon off of safe, and pulling the trigger. This will likely cause the weapon to fire, so care is taken to ensure that the weapon is first pointed in a safe direction.
  The rate of fire may be controlled by three different gas regulator settings. The first setting allows the weapon to cycle at 650–750 rounds per minute, the second setting being 750–850 rounds per minute, and the third setting being 850–950 rounds per minute. These settings are changed by dismounting the barrel, removing the gas regulator collar and turning the gas regulator to allow more or less gas to move through the weapon system. It is generally performed only when necessary to return the gun to operation after fouling has caused sluggish operation and there is no time to properly clean the weapon.
  The barrels can be exchanged rapidly, thanks to a barrel release button located on the left side of the weapon. The weapon is cleared first and then the button is held down, while the barrel's carrying handle is moved from the right side of the weapon to the center, unlocking it from the receiver. At this point, the button is released and the barrel is then pulled free of the receiver and placed to the side. The new barrel is inserted into the receiver and then the carrying handle is shifted to the right, locking it into place. Headspace is set by counting the clicks as the barrel is locked down and should be between two and seven clicks.
  During prolonged firing, care must be taken to not allow exposed skin to come in contact with the weapon. The barrels can become hot enough to inflict second-degree burns instantly without becoming visibly different. These hot barrels g
caption: An M1 Abrams tank with the tank commander's .50-caliber M2 Browning machine gun on the right side of the tank, and the ammunition loader's M240 on the left side of the tank. A second M240 is mounted coaxially next to the main gun
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