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Would you stake your life, right now, on the condition of your equipment?
NEWS | Feb. 14, 2023

M240B Machine Gun: Properly Clean the Gas System to Avoid Malfunction

BLUF: Use the proper tools and these steps to clean your M240 machine gun gas ports.

M240B machine gun
Photo by Sgt. Lianne Hirano

Dear Editor,

The M240 machine gun is gas-operated and fires from the open bolt position. But some operators are failing to clean its gas system properly, leaving the ports on the barrel plugged. This blocks the gas system and causes the weapon to malfunction.
Follow these tips to keep the gas flowing in your machine gun:
  • Make sure you have the combination tool, NSN 4933-01-033-1503, and reamer, NSN 4933-01-047-3394, on hand.
combination tool and reamer
Keep combination tool and reamer handy
  • Clean the gas ports in the barrel using the reamer. Then check down the barrel to see if it’s clear and the carbon is broken up.
Clean using barrel gas port holes
Clean using barrel gas port holes
Use reamer in gas port
Use reamer in gas port
  • Clean the gas regulator next. Make sure to remove all the carbon and built-up copper, inside and out, along the gas regulator cutout and port hole.
Clean M240 gas regulator
Clean M240 gas regulator
  • Then clean the carbon and copper from the guide rod.
  • Finally, clean the gas tube end of the receiver. 
If the M240 gas system isn’t properly cleaned, then the regulator may not fit correctly, and the barrel may not be properly attached to the weapon. That can lead to injury.
Also, pay attention to the barrel threads, receiver and outside chamber end of the barrel while cleaning and maintaining the machine gun. Remove all carbon from these areas. This will help the barrel firmly and properly fit together.  

Clean carbon from receiver and barrel
Clean carbon from receiver and barrel

Fred Fanning II
Mark Haggith

Ft Leonard Wood, MO
Editor's Note: Thanks, gentlemen, for the insightful information. We'll 'gas's it on.
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