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The M240B machine gun is a

belt-fed, air-cooled, gas-operated, fully automatic machine gun that fires from the open bolt position. The M240B machine gun is found in the machine gun section of the weapons platoon of every rifle company in the Marine Corps


What are the Eight Main Components of the M240B medium machine gun

Barrel assembly
Butt-stock and buffer assembly
Driving spring rod assembly
Bolt and operating rod assembly
Trigger-housing assembly
Cover assembly
Feed tray
Receiver assembly


The ammunition is issued in 100-round bandoleers. Weight of a 100 round assault pack (2 per can) is

7 pounds


The five types of ammunition for M240B are

M172 Dummy
M82 Blank
M80 Ball
M62 Tracer
M61/M993 Armor-piercing


characteristics of M172 Dummy are

Fluted cartridge
No primer or propellant


characteristics of M82 Blank are

Double tapered neck
No bullet


characteristics of M80 Ball are

Full metal jacketed bullet


characteristics of M62 Tracer are

Orange tip


characteristics of M61/M993 Armor-piercing are

Black tip on the bullet


the unloading and clearing procedures for the M240B are

Determine if the barrel is hot (200 rounds in 2 minutes or less).
A hot barrel may cause the round to cook off.
If the bolt is not already locked to the rear, pull the bolt to the rear and lock it.
Place the weapon on SAFE
Raise the cover and remove the belted ammunition
Lift the feed tray and inspect the chamber
Close the cover
Place the weapon on FIRE
While holding the cocking handle to the rear, pull the trigger and ease the bolt forward.


General disassembly (field stripping) is the separation of the M240B into

5 main groups


Detailed disassembly involves

removal of component parts of some of the main groups


What are the steps for detailed disassembly of the M240B

Step 1
Remove the spring-loaded pin that holds the bolt and operating rod together
Step 2
Hold the barrel at the point where the gas system attaches to it
Step 3
Grasp and rotate the collar clockwise until it releases from the gas plug. Remove the collar from the gas plug and separate the plug and collar from the barrel. Remove the heat shield by pulling up on the rear of the heat shield, releasing the spring tension around the barrel.
Step 4
Pull the hinge spring pin out and lift the cover and feed tray from the receiver


Before Firing the M240B you

Inspect for cleanliness, proper mechanical condition, and missing or broken parts. Press the barrel release latch and turn the barrel carrying handle clockwise while counting the number of clicks (fewer than 2 clicks or more than 7 clicks indicates a possible barrel defect)


During Firing of the M240B you

maintain a light coat of CLP on the parts listed in the general assembly section above. Ensure that the gas system's connections remain tight. Change barrels when necessary.


After Firing the M240B you

clean the gun with CLP, RBC, or dry cleaning solvent. Even the most careful initial cleaning will not remove all carbon deposits; therefore, you must clean the gun for three consecutive days after firing. After cleaning each day, wipe off all cleaning materials and place a light coat of CLP on all metal parts.


When Inspecting the M240B you

 Always check for cleanliness.
 Look for broken, missing, or burred parts.
 Test the spring tension of appropriate parts, and perform appropriate checks to determine if the gun functions properly


The bipod mount is part of the

receiver group; the operator cannot
remove it. The bipod is held in position by the ball joint that joins it
to the bottom of the receiver


M122 Tripod may be extended and collapsed easily and consists of

 A tripod head
 One front and two rear legs
 A traversing bar


The traversing bar on the tripod connects

the two rear legs


The Pintle mounts the M240B to the

M122 Tripod.


The purpose of the T&E mechanism is to

provide controlled manipulation and the ability to engage predetermined target.


The complete gun bag is used to carry the

 Machine gun
 Tripod
 Pintle
 Traversing and Elevating mechanism
 Spare barrel
 All user maintenance equipment
 Other accessories (SL-3 components)


The removable spare barrel bag is designed for field use and will carry

 The spare barrel
 A complete set of user maintenance equipment and accessories


The ability to quickly change the M240B barrel provides what great advantage

one barrel
can be used while the other is cooling, thus increasing the life of each barrel and
ensuring a continuous rapid rate of accurate fire. Change barrels when they are
beginning to overheat


Two of the more common malfunctions of the M240B are

sluggish operation and runaway gun


Instead of firing at its normal rate (approximately 9 to 10 rounds per second), a sluggish gun fires very slowly due to excessive

Friction usually due to
 lack of lubrication
 excessive dirt/carbon in the gas system or on the bolt and receiver rails
Loss of gas, usually due to
 loose connections in the gas system


Runaway gun is when a gun continues to fire after the trigger is released; firing is uncontrolled. A runaway gun is

 usually caused by a worn, broken, or burred sear; the sear shoulder is unable to grab the operating rod and hold it to the rear
 also cause by an excessively worn sear notch on the operating rod


To stop a runaway gun, for both tripod and bipod-mounted guns, the team leader does what

twists and breaks the belt of ammunition. The remedy for runaway gun is to replace worn parts.


A stoppage is any interruption in the cycle of functioning caused by

 faulty action of the gun
 defective ammunition
In short, the gun stops firing. Stoppages must be cleared quickly and firing resumed.


Immediate action is

action that the gunner/crew performs to reduce a stoppage, without investigating its cause, and quickly return the gun to action. Hang fire and cook off are terms that describe the ammunition condition and should be understood in conjunction with immediate action procedures


A hang fire occurs when

the cartridge primer detonates after being struck by the firing pin but some problem with the propellant powder causes it to burn too slowly and delays the firing of the projectile. Wait five seconds before investigating a stoppage further because if the round goes off with the cover of the weapon open:
 personnel could be injured
 equipment could be damaged


A cook off occurs when

the heat of the barrel is high enough to cause the propellant powder inside the round to ignite even though the primer is not struck. Immediate action is completed in a total of 10 seconds to ensure that the round is extracted before the heat of the barrel affects it


Classification of a Hot Gun/Immediate Action are

 More than 200 rounds fired within a 2 minute period
 A long continuous burst or repeated firing of the weapon even though 200 rounds were not fired
 If the unit leader determines the weapon is hot for any reason.


Classification of a Hot Gun/Immediate Action Step 1 is

Shout, “Misfire!” Wait 5 seconds after the misfire to guard against a hang fire.


Classification of a Hot Gun/Immediate Action Step 2 is

Within the next 5 seconds (to guard against a cook off), pull the charging handle to the rear and observe the ejection port. If brass:
 was seen ejecting, attempt to fire again
 did not eject, place the weapon on “S,” and determine if the barrel is:
o Hot (200 rounds or more fired in the last 2 minutes)
o Cold


When immediate action fails to reduce the stoppage, take

remedial action


Two common causes of stoppage that may require remedial action are failure to extract due to

either a stuck cartridge or ruptured cartridge


Weapons Conditions 1 for M240B is

 Ammunition in position on feed tray
 Bolt locked to the rear
 Weapon on safe


Weapons Conditions 2 for M240B is

 Not applicable to the M240B


Weapons Conditions 3 for M240B is

 Ammunition in position on feed tray
 Chamber empty
 Bolt forward
 Safety not engaged


Weapons Conditions 4 for M240B is

 Feed tray clear of ammunition
 Chamber empty
 Bolt forward
 Safety not engaged