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071-025-0001 (SL1) - Maintain an M240B Machine Gun

Standards: Cleaned and lubricated the M240B machine gun and components. Inspected all parts, components, and ammunition for serviceability; turned in unserviceable items to maintenance. Correctly assembled the gun and ensured it was operational.

Conditions: Given a cleared M240B machine gun; M122A1 tripod mount assembly; linked 7.62-mm ammunition; and a small-arms case with the following items: cleaner, lubricant, and preservative (CLP), lubricating oil arctic weather (LAW), rifle bore cleaner (RBC), rags, pipe cleaners, chamber and bore brushes, cleaning rod, cleaning rags, small-arms swabs, and an M240B scraper and reamer.

Standards: Cleaned and lubricated the M240B machine gun and components. Inspected all parts, components, and ammunition for serviceability; turned in unserviceable items to maintenance. Correctly assembled the gun and ensured it was operational.

Performance Steps

1.   Check to ensure the weapon is clear.

WARNING: Be sure to clear weapon before disassembling, cleaning, inspecting, transporting, or storing.

a. Put safety to "F" (FIRE).

b. Pull cocking handle assembly to the rear, locking the bolt to the rear. Return cocking handle to forward position.

c. Place safety to "S" (SAFE).

d. Push in latches to open cover assembly.

e. Remove ammunition belt, if present.

f.  Raise feed tray.

g. Inspect chamber area. Remove any ammunition, ammunition casings, or links.

(1)  Check feed pawl assembly and feed tray assembly.

(2)  Lift feed tray assembly and inspect the chamber.

(3)  Check space between the face of the bolt and the chamber.

(4)  Check space under the bolt and operating rod assembly.

h. Lower feed tray.

i.   Place safety to "F."

j.   Hold cocking handle assembly to rear, depress trigger, and ease bolt forward to close and lock.

k. Close cover assembly. Make sure it locks shut.

Note. Be sure bolt is forward with safety in "F" when gun is not in use.

2.   Disassemble the M240B.

WARNING: A hot barrel can burn you. If the barrel is hot, use your heat resistant mittens

Note. The following steps do not have to be performed in sequence.

a. Remove barrel assembly.

(1)  Check to ensure bolt is forward.

(2)  Depress barrel locking latch and hold.

(3)  Turn barrel carrying handle to upright position.

(4)  Push forward and lift barrel out.

b. Remove heat shield assembly from barrel. Lift rear of heat shield assembly from barrel; pry front tabs out of holes on gas hole bushing.

c. Remove trigger-housing assembly.

(1)  Depress spring pin and remove it (this can usually be done without tools).

(2)  Pull trigger-housing assembly down and back, and remove it.

d. Remove butt stock and buffer assembly. Depress backplate latch and lift butt stock and buffer assembly straight up.

e. Remove driving spring rod assembly.

(1)  Push driving spring rod assembly forward and up to disengage its retaining stud from the receiver.

(2)  Pull rearward on driving spring rod and remove it from the receiver.

f.  Remove bolt and operating rod assembly.

(1)  Depress cover latches and raise cover assembly.

(2)  Pull cocking handle assembly back to move bolt and operating rod assembly to the rear of receiver.

(3)  Reach into receiver and push rearward on bolt until bolt and operating rod assembly are slightly out of rear end of receiver.

(4)  Grasp bolt and operating rod assembly and remove it from the receiver.

(5)  Return cocking handle to forward position.

g. Remove cover assembly.

(1)  Close cover.

(2)  Push out spring pin as far as possible using backplate of the butt stock or buffer assembly. Then remove it with your fingers.

(3)  Depress cover latches, lift up, and remove cover assembly.

(4)  Remove feed tray.

h. Remove hand guard.

(1)  Extend bipod legs to down and locked position.

(2)  Pull hand guard straight down and off gas cylinder.

WARNING: Using gasoline, kerosene, hydraulic oil, benzene, benzol, high pressure water, steam, or air for cleaning is prohibited

3.   Clean the M240B parts, components, and ammunition.


1. Do not use abrasives to clean the bore, piston, gas cylinder, or gas regulator plug.

2. Do not submerge buffer in any liquid. Wipe with clean wiping rag only.

3. Avoid getting CLP in the gas cylinder when cleaning the bore.

a. Use cleaning patches, CLP, and bore brush to clean bore.

b. Use CLP on receiver brush bristles to clean the receiver.

c. Use rags and CLP to remove powder fouling, corrosion, dirt, and rust from all metal components and surfaces.

d. Use only a clean rag to clean the cover assembly.

e. Clean the gas cylinder.

(1)  Use a gas cylinder cleaning brush dampened with CLP to clean gas cylinder bore.

(2)  Use a combination tool to clean front interior of gas cylinder.

(a)   Insert the combination tool with handle upward into the front end of the gas cylinder of the receiver body. Ensure the tool is fully inserted and seated against the gas cylinder.

(b)   Apply slight pressure to the handles and turn clockwise to remove carbon.

f.  Clean gas regulator using the scraper and reamer.

(1)  Insert the scraper into the central hole of the gas regulator plug. Remove carbon by twisting the scraper clockwise until it is fully seated against gas regulator plug.

(2)  Clean regulator plug grooves by inserting the scraper tool into the grooves and turning regulator plug clockwise.

(3)  Insert the small reamer into each gas inlet hole and twist back and forth to remove carbon (use hand pressure only).

(4)  Scrape carbon from surface of gas regulator plug using tip of scraper.

(5)  Insert large reamer through hole in gas port bushing into gas port hole in barrel; remove carbon by twisting reamer back and forth until it enters bore of barrel.

g. Clean M122A1 tripod assembly.

(1)  T&E mechanism. Use a clean dry wiping rag to remove foreign matter. Use small arms cleaning brush to clean numbers on the scale.

(2)  Tripod assembly and flex mount. Use a cleaning rag saturated with carbon-removing compound to clean them with clean wiping rags to wipe all parts dry.

h. Clean Ammunition. Use a clean dry wiping rag to remove foreign matter.

4.   Inspect the M240B parts, components, and ammunition.

a. Barrel assembly.

(1)  Check barrel for bulges, bends, burrs, or pits in the chamber or bore.

(2)  Check to ensure flash suppressor is not loose.

(3)  Check front sight for damage and looseness.

(4)  Check barrel carrying handle assembly for damaged or missing parts. Move the barrel release slowly to the right and count the clicks. Fewer than two, or more than seven clicks indicate defective parts.

(5)  Check to ensure heat shield is present, securely attached to barrel, and undamaged.

b. Butt stock and buffer assembly.

(1)  Check for burrs and rough edges on the mating grooves and flanges.

(2)  Check the backplate latch to ensure it locks the buffer assembly securely.

(3)  Check the buffer plug and ensure it sticks out through the backplate and is flush or higher than the protrusion below it.

(4)  Check the buffer for rattling sounds by shaking; ensure that the plug cannot rotate by finger pressure.

(5)  Check the butt stock for cracks.

c. Driving spring rod assembly.

(1)  Check the spring for broken strands.

(2)  Check the rod assembly for bends.

d. Bolt and operating rod assembly.

(1)  Inspect the bolt and operating rod assembly for bent, broken, cracked or missing parts. Check for burrs or pits on the surface.

(2)  Check for cracks or wear on the tip of the firing pin.

(3)  Ensure you cannot move extractor with your fingers.

e. Trigger-housing assembly

(1)  Check for broken, missing, or damaged parts.

(2)  Inspect the tripping lever and sear for burrs on edges.

(3)  Check cocking action by pushing back on the tripping lever (sear will rise). Pull the trigger (sear will lower).

(4)  Check safety. Place on "S" (SAFE) and pull the trigger. The sear should not drop down far enough to lock in the downward position. Place the safety on "F" (FIRE) and pull the trigger. The sear should drop down and lock in the downward position.

f.  Cover assembly.

(1)  Pivot the feed lever back and forth to ensure it operates smoothly without binding.

(2)  Push in on the cover latches to make sure the retaining clip is present, secure, and does not bind in the housing.

(3)  Push down on the cartridge guides and feed pawls to make sure the springs are present and secure.

(4)  Inspect accessory-mounting rail for nicks or burrs.

g. Feed tray. Check for cracks, deformation, broken welds, and loose rivets.

h. Hand guard. Check for cracks and broken or missing parts.

i.   Receiver assembly.

(1)  Check that the rear sight is securely mounted and operates properly.

(2)  Check that the cocking handle operates properly.

(3)  Check for damaged or missing ejection port cover, spring, and pin. Check for proper operation of ejection port cover.

(4)  Lower and raise the bipod legs to ensure they move freely without binding.

(5)  Check accessory-mounting rail for nicks or burrs that may prevent proper attachment of optional sighting devices.

(6)  Check barrel locking latch and cover detent for proper spring tension.

j.   Components.

(1)  T&E mechanism.

(a)   Inspect hand wheels for smooth operation or rust.

(b)   Check threads for burrs and rust.

(c)   Check traversing slide lock for spring action. Ensure elevating mechanism sleeve fits on traversing bar and clamps firmly.

(d)   Check traversing and elevating scales for legibility.

(e)   Inspect quick release pin and chain for burrs and rust. Check for missing spring-loaded balls.

(2)  Tripod assembly.

(a)   Check for completeness of tripod. Ensure that all nuts and bolts are tightly secured.

(b)   Inspect for cracks on the legs and tripod head.

(c)   Check for missing, broken, or inoperative lock latch.

(d)   Check pintle lock release cam for correct operation.

(e)   Check locking action of front leg clamping assembly.

(f)    Check that the rear legs lock in the open position. Ensure sleeve latch notch and right leg slide notch engages completely. Ensure latch spring has good tension.

(g)   Check telescoping, indexing, and locking action of rear legs and front leg locking assemblies.

(3)  Flexible mount assembly.

(a)   Check for missing or damaged parts. Check for rust, cracks, and burrs.

(b)   Inspect pintle lock assembly for nut, bolt, and cotter pin. Check pintle surface for burrs and rust.

k. Inspect or check ammunition for damage and corrosion. Turn in any unserviceable ammunition.

5.   Lubricate M240B parts and components.

a. Generously lube the following parts:

(1)  Barrel assembly-on the camming surfaces of the bolt-locking lugs.

(2)  Operating rod-on the rollers, camming recess, and those surfaces immediately below the yoke that ride within the receiver rails.

(3)  Cover-in the feed cam assembly.

(4)  Bolt-on the bolt-locking lugs and actuator cam roller.

b. Lightly lube the following parts:

(1)  Driving spring.

(2)  Bolt and operating rod assembly moving parts, polished areas, firing pin, and roller.

c. Do not lubricate the following parts:

(1)  Butt stock.

(2)  Face of bolt.

(3)  Piston.

(4)  Gas regulator and gas cylinder.

(5)  Rear sight.

(6)  Composite or rubber components.

d. Lightly lubricate all components and wipe with oily rag to remove excess oil.

6.   Assemble the M240B.

a. Replace barrel assembly.

(1)  Insert gas regulator plug into the gas hole bushing with the number 1 gas setting facing the barrel.

(2)  Place gas collar over the front end of the gas regulator plug. Rotate collar until it slips onto gas regulator plug. Press in and rotate counterclockwise to lock in place (pull collar to be sure it is in the locked position).

(3)  Install heat shield on barrel. Insert the front metal tabs of the heat shield into the holes located on the sides of the gas hole bushing. Push down on the heat shield so it snaps onto the barrel.

(4)  With gas regulator downward and the carrying handle in the vertical position, insert barrel fully into the receiver socket and push barrel carrying handle to the right as far as it will go to lock (fewer than two or more than seven clicks indicate defective parts). Do not force. If barrel binds in socket or if barrel carrying handle will not rotate when pushed, do not pound on barrel carrying handle. Take machine gun to unit maintenance.

b. Replace cover assembly and feed tray.

(1)  Align the feed tray guides with receiver brackets.

(2)  Place cover assembly onto the receiver with its mounting holes aligned with mounting brackets on the receiver.

(3)  Close cover assembly. To secure the cover and feed tray to the receiver; insert the spring pin in the mounting holes from the right side only. Open cover assembly. Check to ensure cover detent holds cover assembly open. If cover assembly does not remain open in two positions, notify unit maintenance.

c. Replace trigger-housing assembly.

(1)  Insert the holding notch on the trigger-housing into the forward recess on the bottom of the receiver.

(2)  Lift the trigger-housing up and align holes of trigger-housing with the mounting holes of the receiver.

(3)  Hold the trigger-housing in place and insert the spring pin.

d. Replace bolt and operating rod assembly.

(1)  Insert the bolt and operating rod assembly into the rear of the receiver. Ensure bolt is on top of receiver rails.

(2)  Push the assembly into the receiver as far as possible. Pull the trigger and hold it while pushing the assembly all the way into the receiver.

(3)  Close cover assembly.

e. Replace the driving spring rod assembly.

(1)  Insert driving rod spring assembly all the way into the receiver.

(2)  Push in and lower driving rod spring assembly to seat the retaining stud in the hole on the bottom of the receiver.

f.  Replace butt stock and buffer assembly.

(1)  Position the bottom recess grooves of the butt stock onto the top of the receiver recess grooves.

(2)  Slide the butt stock down until it locks on the receiver. Top of buffer should be flush with top of receiver.

7.   Perform a function check to ensure the M240B is assembled correctly.

Evaluation Preparation: 

Setup: At the test site, provide all the equipment and materials listed in task conditions. Use only dummy ammunition for training purposes.

Brief Soldier: Tell soldier to perform maintenance on the M240B and linked 7.62-mm ammunition.

Performance Measures



1.   Checked to ensure the weapon was clear.



2.   Disassembled the M240B.



3.   Cleaned the M240B parts, components, and ammunition.



4.   Inspected the M240B parts, components, and ammunition.



5.   Lubricated M240B parts and components.



Evaluation Guidance:  Score the soldier GO if all performance measures are passed. Score the soldier NO GO if any performance measure is failed. If the soldier scores NO GO, show him what was done wrong and how to do it correctly.







FM 3-22.68



TM 9-1005-313-10