How To Set Your AR-15 On Fire

Today I shot a Spike’s Tactical midlength AR-15 until it caught fire. The MOE handguard caught fire, that is.

I posted some photos on Facebook, and naturally, it garnered some attention. There were a number of comments about how MOE handguards suck, or plastic sucks, or that normal ARs suck. I am not very concerned about the lamentations of the ignorant, but I would like to address the comments about Magpul products from a quality standpoint.

First, I’ve tested normal and MOE handguards, as well as KAC aluminum handguards, from a heat dissipation standpoint in the past. In my opinion, of the polymer handguards tested, MOE handguards provide the best balance between protecting the shooters’ hands and allowing the handguard and barrel to cool as quickly as possible.

Second, this MOE handguard caught fire the second time my friend Paul and I fired 500 rounds through it in under 5 minutes (semi auto). It cooled fully after the first time, because I put it in some muddy water. It started “breathing.”

Then we loaded mags again and fired the second 500 rounds. At approximately 430 rounds, the handguards caught fire. We stopped to take pics, then kept shooting. We caught up to 500, then tossed it in water again.

This “exercise” is far more than any AR-15 would ever see during normal use. The AR, and M16/M4, are rifles, not light machine guns. I do not think it should reflect negatively upon the MOE handguards that they caught fire. The barrel, gas block, and gas tube were incredibly hot. The receivers of the rifle were too hot to touch with bare hands. The barrel would melt or set fire to any normal object it touched – there will be some cool followups on this.

No one should avoid MOE handguards because of this occurrence.

34 thoughts on “How To Set Your AR-15 On Fire”

  1. Why am I not surprised people have taken this as an opportunity to knock them. Interesting and fun, but as you acknowledged, very unrealistic. If you’re shooting that much that fast it’s probably game over, especially considering a “combat load” is less than half that.


  2. The really interesting part is that this happened the second time. Was it just hotter the second time through, or do you think that getting so hot initially has an effect on the material — one that persists through the cooling cycle — lowering the temperature at which it will combust?

  3. All I’m asking, is when are you going to do the same test on a piston gun. (I’m not trying to start a dust storm, just interested in a comparison) Thanks!

    1. I don’t think you understand the differences between DI and op rod systems… DI is not what set that gun on fire.

      I would suspect that an op rod gun which vented gas inside the handguards (ala LWRC M6 or the new M6-SL) would set the handguards on fire *faster* than a DI gun.

      I personally don’t shoot my LWRC without gloves anymore, having been burned and cut by the gas venting under the rail.

    2. AR-15’s are not DI guns they are considered piston guns. Drives me nuts so called experts don’t know this. The question still comes up and the debate rages on- “Should I Get a Piston for my AR or Direct Impingement?” The answer is- and always has been- very clear- your AR upper already has a piston. Also the AR is not a conventional Direct Impingement system.

      First, let’s take a look at a conventional Direct Impingement system. The DI system uses the expanding gases to act directly on the carrier. The gas travel down the tube and hits a small cylindrical piston that’s part of the carrier and drives it rearward to unlock the bolt.

      his differs from the AR gas system. The piston (the cylindrical protrusion) of the DI system is part of the carrier and the cylinder (the cup the piston fits into) is part of the gas tube. The AR piston is part of the bolt and the carrier is the cylinder.

      Eugene Stoner said in the original patent for his gas sytem “This invention is a true expanding gas system instead of the conventional impinging gas system.” The gases enter the expansion chamber inside the bolt carrier (the cylinder) and drives the carrier rearward as the piston as part of the bolt, is locked into place. The rearward motion continues, unlocking the bolt and extracting the spent case.

      The system is designed to be self regulating. When enough pressure enters to operate the action and the carrier begins to move, the key separates from the tube and cuts off the gas flow to the carrier. There are also vents in the carrier to allow the gases to escape and the pressure to drop inside the cylinder when the piston seals move past them. After that, the action is powered by momentum and returned into position by the energy stored in the action spring.

      In the AR system, Eugene Stoner eliminated the actuator rod of other piston gas systems and incorporates the piston with the bolt and the cylinder with the bolt carrier to “…provide smoother operation and longer life of the working parts…” The patent goes on to explain that since all the actuating force is inline with the bore and bolt to the shooter’s shoulder “all of the off center loads found in most other types of gas actuated weapons are eliminated” to cut down on “climb” during automatic fire.

      The so-called “piston upper” (ie- Adams, HK416, LWRC etc.,) does not convert an AR from direct impingement system to a piston system. It converts the AR from an inline piston system to an offset piston system and adds an actuator rod.

      Anyone tells you your AR needs a piston to run cleaner/cooler/tacticooler, tell them “No thank you. My AR already has a piston”

      Stoner Patent #2,951,424:…page&q&f=false

      1. “AR-15′s are not DI guns they are considered piston guns. Drives me nuts so called experts don’t know this.”

        I have been known to go on a very similar rant when somebody points me to a Throttle Position Sensor on a diesel engine.
        You see diesels don’t have throttles…

        1. They do now! All the modern diesels in production on road vehicles now do have throttles on them for airflow control and emissions reasons.

  4. It’s pretty funny to see all the people focusing on the MOE or the DI system as somehow flawed because of this test. Put enough rounds through any firearm in a short enough time and this will happen. Even piston driven weapon systems with non polymer forends:

    I think the lesson here (if there is one) is that if you want to shoot a lot of rounds quickly over a sustained period… get a Vickers gun.

  5. Holy crap. It’s idiotic that people are bashing MOE handguards though. Even legendary Colt handguards will eventually burn, like in the video of a M4 being fired to destruction.

  6. Questions to think about more than i’m looking for hard answers:

    What catches fire first if there is no handguard?
    Didn’t DPMS have/sell an aluminum ring of rods style handguard?
    What would/does happen to carbon fiber when exposed to these temps? It doesn’t really ignite, but can oxidize if enough heat/burning fuel is applied

  7. I’m surprised the gas tube survived long enough to let it get that hot. At Cav Arms about 9 years ago we did multiple full auto beta mag dumps through an M16 to try to melt some C4/M4 style handguards and the gas tube melted down first and only melted the handguards where it contacted them.

      1. I don’t think the finish on it made a different. Being a quality gas tube is what made the difference. If you notice when testing is done on Colts, or other quality AR15s the barrels fail before the gas tubes. However when these similar tests were done with cheaper uppers(DPMS, some Bushmasters, etc), the gas tubes failed first. I don’t know how to tell the difference, but I believe that there is a quality difference between various brands of gas tubes.

  8. This makes me extra happy that I just bought a Spike’s Tactical M4. I haven’t heard anything negative about the function of the rifle, and this just convinces me more that I made a good purchase.

    1. Something I just thought of though…isn’t there a chance that the sudden superheating and then sudden cooling of the firearm could do bad things to the heat treatment of the metal and cause a catastrophic failure in the future? I don’t know if the temperatures involved is extreme enough, but it seems worth looking into.

  9. The moe handguards are designed and tested to remain functional under the US Military’s recommended sustained firing guidelines…

    The current sustained rate of fire for the M4A1 Carbine is 15 rounds per minute and a maximum rate of 90 [rounds] per minute for short periods in an emergency.” Firing the M4 carbine at cyclic rates of fire of 90 to 150 rounds per minute, “which is the rate of suppressive fire associated with machine guns” for prolonged periods leads to rapid heating of the barrel and possible failure.

    USSOCOM SOPMOD Program Office (USPO), (23 February 2001). M4A1 5.56mm Carbine and Related Systems Deficiencies and Solutions: Operational and Technical Study with Analysis of Alternatives (Draft, Version 6), (Crane, Indiana: Naval Surface Warfare Center USPO, 2001), p. 16.

    1. Yes, the other MOE-equipped rifles are being shot at the US Military maximum sustained rate of fire and no issues have been observed.

  10. This was certainly an entertaining video. I won’t avoid MOE handguards because of it, although sadly I already avoid them because I find them too big around for me to comfortably grasp.

  11. Do you have any vid of you shooting till the handguards actually caught on fire? I ask because there is a vid of someone shooting an AK till the wooden handguards catch fire and it’s often used as “Look the AK is superior.” Id like to show than an AR can do that too. Just like your dust test video with the 5.45 upper.

  12. Andrew, i’m looking to pick up another upper/rifle to go along with my ddm4. I’ve been looking at bcm mid length upper. 1) it’s something different 2) softer recoil impulse will hopefully help me to get my girlfriend to shoot more. At the same time, i would like the rifle to be dependable. Your above video goes towards getting me that peace of mind. I know that you have shot over 2k rounds of steel cased ammo through one of your ar-15 without lubrication/cleaning before experiencing malfunctions, have you tried a similar test with a mid length gas system gun? And if not, what has your experience been in shooting steel cased ammunition through 16 inch mid length guns?

    1. The rifle shown in this post is a Spike’s midlength shooting Tula ammo. It remains functional and serviceable.

  13. Any idea what causes the “breathing” effect? I could understand it if water was entering, the exiting, but it didn’t look like that was the case.

    1. I believe water entering the bore and then boiling, leaving space for more water to enter and the cycle repeats.

  14. Thanks for the backstory on the FB pics. I have heard of guys calling various manufacturers, complaining that the gas tubes melted when they used a full auto lower on their upper, and went cyclic, but not catching handguards on fire.

    BTW, did the ‘tempering’ have any effect on the metal of the weapon?

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