In my Three Day Patrol Carbine Course, I cover quite a few topics, specifically concentrating on end user needs.  Maintenance is always covered. I like to clean quickly while being thorough. During cleaning, it’s important to check key areas to ensure your platform will continue working for you.

Make no mistake, I like a quality carbine/rifle.  It’s my life, so I don’t take short cuts.  No matter which make/manufacturer you choose, you need to care for your weapon no matter which manufacturer you choose.

In this article, I will address the bolt and gas rings.  If you extend the bolt from the Bolt Carrier Group and place it on a flat surface the bolt  should support the weight of the BCG. If the BCG collapses, that is an indicator to change the gas rings.  Another variation is to close the bolt and hold the bolt and suspend it vertically.  The BCG should not move.

In a recent class, four students from a neighboring SWAT Team performed the test and all BCG’s collapsed.  I examined the BCG’S and bolts.  It appeared as though the manganese phosphate (parkerized) finish had been removed with a brush attached to a Dremel tool.  The tail of the bolts had been polished to a sparkling finish.  The gas rings had been damaged by the high speed Dremel.  The students said the weapons were “hand me downs and had been in service since 1999.”  The extractor springs were worn and had blue inserts.

I changed out the gas rings and replaced the extractor springs and inserts. The current mil spec extractor insert is black on both carbine and rifle. Colt has produced a new spring.  It is stronger and provides more tension.  No O-ring needed.  The extractors however looked serviceable.

After applying lubrication to the bolts, we conducted test fires and all the weapons worked.  I recommended that they think about replacing the bolts as the had been polished to a high gloss finish.  Bolts are generally shot peened for strength and manganese phosphate is applied as well to the surface.

The gas rings take a lot of abuse.  Quite a bit of friction develops there.  If you are doing a lot of rapid fire on either semi or Group Therapy (Full Auto,) the gas rings will wear faster.  A lot of theories are out there on lubricating the AR platform.  CLP, Synthetics and now Green Lube products.  I have used Breakfree CLP in a lot environments.  It works well for me.  What ever you use, test it and make sure it holds up.  Recently I observed an shooter dip a BCG into a coffee can filled with motor oil.  File under Valdez Oil Spill.  Not recommended.

Will over lubrication cause an AR to Fail?  Generally no.  However the weapon will eventually cool and the lubricant may have possibly picked up debris. This will solidify.   The “sludge” then causes parts to not work reliably.  Think of the disconnector sitting on top of the trigger.  A small spring on the trigger applies tension to the disconnector.  This becomes an issue if you are running a burst configuration.

Not long ago, a government unit called into the factory and said that the weapon was running in semi but failed to go through the three round cycle. The issue was put out to the instructors.  Dean Caputo and I, both asked if heavy lubrication had been applied.  “Yes.”  was the reply. Both of us recommended the same solution: Disassemble the gun and clean the parts. When checking the fire control group, the armorer found that the two disconnectors had become stuck. Applying a healthy dose of Hoppes # 9 to all parts solved the problem.  The parts were placed back in the weapon and it functioned. LIGHT lubrication!

I like to put two drops in the visible hole on the BCG when the ejection port cover is open.  Then work your charging handle several times.  I do this when going on a job.  If your  carbine is sitting in the trunk, some issues can crop up. Depending what part of the country your are working in.   Humidity and extreme temperature  change  can cause the lube to evaporate.  If you are heading out to the range and the weapon has been stored, same suggestion.  Two drops in the bolt and you should be fine.

If a gas ring breaks, the weapon will still run.  Change out the rings as soon as feasible.  Replacing three gas rings is the rule. If one has failed the others are suspect.

My blow out kit for the carbine includes gas rings, extractor and springs w/insert and spare firing pin. These fit nicely in a Tango Down Grip.  MagPul grips have the same storage space as well. Raid the CSI van at the next crime scene.  They have those nice small evidence zip loc bags.  Perfect for small parts. Take care of your gas rings, lubricate properly and you will be well on your way to keeping your carbine reliable.




This entry was posted in AR15/M4, Weapon Maintenance by Frank Moody. Bookmark the permalink.

About Frank Moody

Frank Moody is a 32-year LEO veteran on a major Northeast Agency. He has worked Patrol, Traffic Motorcycle, Narcotics Organized Crime, Fugitive Operatons and SWAT. During his career, he has become an authority in Firearms Tactical Training and is a Force on Force instructor. Frank is a Factory Armorer Instructor on AR/M16/M4 platforms, the 1911 Pistol and the 203 Grenade Launcher.

11 thoughts on “THE M4 BOLT: GAS RINGS

    • Your welcome Robert. Class postings are coming out in the next day or so.

  1. What is the opinion(s) on the one-piece McFarland gas ring, as ooposed to the three ring setup ?

    • I haven’t used the one piece ring, nor have I known anyone who really has. The standard 3 ring setup works well, so it is not one of the areas I concentrate on when setting up a gun.

  2. As Hilton stated, the standard as ring setup works quite well. Contrary to popular belief, you DO NOT need to stagger the gaps in the gas rings for proper function. Dean Caputo has demonstrated in his classes that the M4 platform will run just fine with only ONE gas ring installed. Proper maintenance and inspection is all that’s required.

    • Tim
      I would mirror your comment that the gun will run with one ring intact and without staggering the rings. Old Wives Tales and Urban Legends Die Hard.

      I had a students rings break and tie up his carbine in a class. I pulled the broken rings, and to prove the point put him back on the line with one ring. The gun ran fine, to the amazement of some of my fellow instructors.

      Keep it moderately clean and lubed and a quality weapon will run.
      Be Safe

  3. Good article, dremel usage and not realizing collapsing Bolts being a bad thing are unfortunately things you still see from time to time with working handlers of the black rifle. Usually stems from shaky knowledge that someone passed onto them.

  4. A late question; I was trained to hold the BCG vertically, without firing pin or bolt cam pin, and if the bolt can slide out from it’s own weight then it’s time to change gas rings.
    Since the bolt carrier is heavier than the bolt, standing the BCG on the face of the bolt would give an indication for change of gas rings a lot sooner than what I had been taught. I don’t know what round count would separate these two, but still. Any thoughts?

    • Soren, I’ve been shown two ways by various Colt Armorer Instructors: Frank pretty much covers it in his article above. One way is to stand an assembled bolt on its face with the bolt extended. If the carrier slides forward, the gas rings need replacement. The other way is to collapse the bolt and hold it vertically by the the bolt and let the carrier dangle. If the carrier slides down, then, well, you know the rest. Either way is functionally similar and will give a good indication as to whether or not the gas rings are excessively worn. Your method deletes the friction from the cam pin which would actually provide less resistance than the above listed methods. However you do it, they are pretty darn close.

      • Great article! I cannot tell you how many stories I have heard of M16/AR15/M4 reliability problems. In every case when I looked at the rifle( if they actually owned one) there were glaring problems with the gun. I Have neglected one of my guns for 2000 or so rounds and it performed perfect!
        Proper maint. and lubrication is all you need!

Comments are closed.