M240 G Class Machine Gun

United States Marine Corps

Weapon Systems Series

M240 G

RoleThe M240G supports the infantryman in both the offense and the defense by providing a heavy volume of accurate, long-range fire beyond the capability of individual small arms.

Major Components of the M240G This diagram and table identify the major components of the M240G.

Number Name of Component
1 Barrel group assembly
2 Buttstock and buffer assembly
3 Drive spring rod assembly
4 Bolt and operating rod assembly
5 Trigger housing assembly
6 Cover assembly
7 Feed tray
8 Receiver assembly

Weight

The following table lists the weight (in pounds) of the M240G.

Item Weight (in pounds)
Weight of machinegun 25.6
Weight of tripod, M122 flex mount, and T&E (complete) 20
Weight of spare barrel case (SL-3 complete) 12.9

Dimensions

The following table lists the dimensions (in inches) of the M240G.

Item Dimension (in inches)
Overall length of the gun 49
Rifling 4 grooves with uniform right-hand twist (1 turn per 12 inches)
Height of machinegun on M122 tripod 17

Manipulation

The following table lists the traverse limits for the M240G (with M122 tripod Limits of M122 with traversing and elevation (T&E) mechanism). Tripod

Item Limits
Elevation 247 mils (18 degrees)
Depression 200 mils (11 degrees)
Traverse (traversing bar) 875 mils (49 degrees)

Rates of Fire

The following table lists the rates of fire for the M240G.

Method of Delivery Rates of fire (in rounds per minute)
Cyclic 650-950 (depends on gas setting) on continuous burst
Sustained 100; 6-8 round burst (4-5 seconds between bursts)
Rapid 200; 10-12 round burst (2-3 seconds between bursts)

Range

The following table lists the range limits (in meters) for the M240G.

Range Limits (in meters)
Maximum 3,725
Maximum effective (area) 1,800
Maximum effective (point) 800
Tracer burnout Approximately 900
Grazing fire 600

Three Descriptive Characteristics

Three descriptive characteristics of the M240G are that it is:
Belt-fed. The gun is fed by a disintegrating metallic link belt.
Gas-operated. The gas produced from firing one round provides the energy to mechanically prepare the weapon to fire the next.
Air-cooled. The barrel and receiver are exposed to permit cooling by the air.

Eight Steps

The cycle of operation for the M240G consists of eight sequential steps listed in the table below.

Step Action
Firing After the bolt reaches its locked position, the operating rod moves forward, independent of the bolt. It carries the striker of the fixed firing pin through the aperture in the face of the bolt, striking and detonating the primer of the cartridge.
Unlocking After the cartridge ignites and the projectile passes the gas port, part of the gases enter the gas cylinder. The rapidly expanding gases enter the hollow end cap of the gas piston and force the operating assembly to the rear, providing the power for the last four steps in the cycle of functioning. The operating rod now moves rearward, independent 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 clears the barrel socket.
Extracting The extractor grips the rim of the cartridge as the bolt and operating rod pull the case from the chamber.
Ejecting As the case is withdrawn from the chamber, the ejector exerts a push from the top, and the extractor exerts a pull from the bottom. The casing falls from the gun as soon as it reaches the cartridge ejection port. At approximately the same time, the empty link is forced out of the link ejection port between the cartridge stops on the feed tray by the next round moving into the feed tray groove.
Cocking This is the process of placing the parts of the gun in position to fire the next round. During the rearward independent movement of the operating rod, the firing pin striker is withdrawn from the face of the bolt. When the bolt has moved far enough to the rear to pick up the next round for chambering, cocking is completed.
Feeding When the bolt is to the rear, the outer feed pawls are outside the first round of ammunition. The inner feed pawls are between the first and second rounds. As the bolt moves forward to fire the round in the feed tray groove, the belt feed pawl moves to the left. It moves up and over the second round in the belt of ammunition and is now in position to drag the second round into the feed tray groove. As the bolt moves to the rear after firing, the belt feed pawl moves to the right, dragging the second round into the feed tray groove. Inside the cover the cam roller, the feed arm with control spring, the feed arm fork, and the pivot arm are present only so the feed pawls can move back and forth, dragging rounds into position to be chambered.
Chambering This is the process of stripping a round from the belt and seating it in the chamber. As the bolt travels forward, the upper locking lug of the bolt contacts the base of the cartridge. The bolt strips the round from the belt link. The chambering ramp angles downward and forces the round toward the chamber along with the spring tension of the cartridge guide pawl. 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.
Locking During chambering, the bolt enters the barrel socket as the operating rod is driven forward by the drive spring and the locking lever, which the bolt is riding on, swings forward pushing the bolt forward and locking it to the barrel socket. Although the term locking is used here, it should be noted that in the M240G the bolt and barrel do not physically interlock. This is why the barrel can be removed even when the bolt is forward.

Types of Ammunition

Ammunition is issued in a disintegrating metallic split linked belt. The members of machinegun teams must be able to recognize the types of ammunition and their use. The table below lists the ammunition for the M240G:

Type and Illustration Color of Tip Used for
Ball (M80) Plain (No color) Marksmanship training Anti-personnel Light material targets
Tracer (M62) Orange Observing fire Incendiary effect Signaling Marking targets
Armor-Piercing (M61) Black Lightly armored targets
Blank (M82) No bullet (metal case with no projectile) Simulated firing
Dummy (M63) No color; fluted cartridge case Gun drills Training (completely inert)

Bipod

The bipod mount is part of the receiver group. The bipod yoke fits around the receiver. The forward grip assembly holds the bipod yoke in position.

To lower the bipod legs, push in on the leg support lock and rotate the legs down and forward as shown in the diagram below.

Note: The legs will automatically lock in the down position.


M122 Tripod The M122 tripod mount consists of the tripod assembly as shown in the diagram below. The M122 provides a stable firing base for the M240G.


Traversing Bar The diagram below shows how the traversing bar connects the two rear legs and supports the traversing and elevation (T&E) mechanism. The traversing bar has a mil scale engraved on it to help the gunner adjust the gun. Engraved on the bar is a scale that measures direction in mils. It is graduated in 5-mil increments and is numbered every 100 mils.


Traversing and The T&E mechanism shown in the diagram below provides controlled Elevating manipulation and ability to engage predetermined targets. (T&E) Mechanism


Adjusting the T&E

  • Traversing Handwheel: Each click of the handwheel indicates a 1 mil change in direction. The total traverse on the screw is 100 mils.
  • Elevating Handwheel: Each click on the handwheel indicates a 1 mil change in elevation. The total change in elevation is plus or minus 200 mils.
  • Flex Mount The flex mount joins the gun and T&E to the tripod to enhances the stability Assembly and dampens the recoil of the weapon as shown in the diagram below.


    Mounting the The preferred method is to mount the flex mount assembly first to the tripod
    M240G and then mount the machine gun. The table below lists the steps to mount the
    M240G.
    Step Action
    1 Lock the M122 tripod’s legs open.
    2 Center the T&E before mounting. Do the following. n the Elevating handwheel, turn until approximately two fingers are visible on upper elevating screw. Traversing slide, rotate until approximately two fingers are visible on lower elevating screw. Traversing handwheel, turn until the offset head is centered on the traversing screw.
    3 Mount the flex mount assembly on the tripod. Place the pintle assembly of flex mount assembly into the sleeve bushing of the tripod. Engage the pintle locking lever to hold the pintle assembly in place.
    4 Mount the T&E mechanism. Lower the traversing slide over the traversing bar. Turn the locking lever to secure the traverse slide in place. Note: See diagram above.
    5 Attach the gun to the flex mount by Aligning the mounting hole Inserting the retaining pin, thereby locking the weapon in place as shown in the diagram below

    Procedure Before you begin disassembling the M240G, you must clear the weapon to be sure it is safe. The following table lists the steps to clear the M240G.

    Step Action
    1 Point the weapon down range or in a safe direction.
    2 Attempt to move the safety to the F position as shown in the picture below.
    3 Pull the cocking handle to the rear until the bolt locks as shown in the picture below.
    4 Return the cocking handle forward and move the safety to the S position as shown in the pictures below.
    5 Push in the latches to open the cover assembly as shown in the picture below.
    6 Raise the feed tray and visually inspect the chamber as shown in the picture below.
    7 If the chamber is clear Place the safety on the fire position (F). Pull the cocking handle to the rear (palm up). Ease the bolt forward by pulling the trigger. Note: Ease the bolt forward to prevent damage to the bolt and barrel.
    8 Close cover assembly.

    Field Stripping After you have cleared the weapon, you can begin to field strip the machinegun into its five major groups as follows:

  • Barrel
  • Trigger housing group
  • Buttstock
  • Receiver group
  • Operating group
  • Removing the Barrel The following table lists the steps for removing the barrel.

    Step Action
    1 Depress and hold the barrel locking latch as shown in the picture below.
    2 Simultaneously rotate the barrel carrying handle assembly.
    3 Remove the barrel by pulling it straight out as shown in the picture below.

    Removing the Trigger Housing Group The following table lists the steps to remove the trigger housing group.

    Step Action
    1 Depress the spring pin as shown in the picture below.
    2 Remove the spring pin as shown in the picture below.
    3 Pull the trigger housing group back and down as shown in the picture below.

    Removing the Buttstock The following table lists the steps to remove the buttstock.

    Step Action
    1 Completely depress the buttstock release latch as shown in the picture below.
    2 Lift the buttstock while holding the receiver with your free hand as shown in the picture below.

    Removing Receiver Group The following table lists the steps to remove the drive spring.

    Step Action
    1 Push the drive spring up and back as shown in the picture below.
    2 Lift the operating rod out of the receiver as shown in the picture below.
    3 Depress the cover latches and raise the cover assembly as shown in the picture below.
    4 Pull the cocking handle to the rear as shown in the picture below.
    5 Slide the bolt and operating assembly to the rear and remove them as shown in picture below.
    6 Close the cover and push the spring pin out with the back of the buffer and remove it as shown in the picture below.
    7 Depress the cover latch and remove the cover assembly and the feed tray assembly as shown in the picture below.

    Gas System Rotate clockwise and remove the collar and the gas regulator assembly from the gas plug. Slide the gas plug to the rear as shown in the picture below.

    Components The spare barrel case should contain each of the following as shown in the figure below.

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