M4 Carbine torture test

The NYTimes.com has published two videos recorded by Colt Defense. They compare the M4 and the M4A1.

M4A1 still going after 911 rounds (although gas tube melts preventing semi or full auto fire)

The NYTimes reports

That video shows the same test with an M-4 equipped with a thicker, heavier barrel, which is used on a specialized carbine, known as the M-4A1. This variant is carried by some Special Operations users.

Colt Defense and the Army have been discussing making the change to a heavier barrel for several months and appear likely to begin requiring standard-issue rifles to have the barrel previously manufactured for the M-4A1.

Sounds like Colt is going on the PR offensive.

[ Many thanks to all the readers who emailed in these videos. ]

Steve Johnson

Founder and Dictator-In-Chief of TFB. A passionate gun owner, a shooting enthusiast and totally tacti-uncool. Favorite first date location: any gun range. Steve can be contacted here.


  • Redchrome

    Not much of a ‘PR Offensive’ considering that piston-driven ARs will easily go 1000 rounds without rupturing a gas tube like that.


    It’s also noteworthy that the gas tube had cracked well before the final failure. The flames on the handguard being blown out, as well as the progressive slowing of the rate of fire, would seem to indicate to me that the gas tube was split and the split growing.

    The M4 isn’t quite as bad as it used be to tho!

  • D

    Moral of the Story: your M4 isnt a SAW

  • ThomasL

    Neither of these seem like terribly likely scenarios. All things being equal, longer sustained fire is better, no objections to that at all, but ~530 rounds is 18 magazines.

    It is hard to imagine any circumstance where someone could go through 18 magazines that quickly, much less a circumstance where they need to go through more than 18 magazines (~530rds) but less than 31 magazines (~911rds).

  • Lance

    The article also states that the M-4A2 will have a M4A1 style heavy barrel to them. The army has stated that a piston right now is only optional in the M-4A2 compation.

  • HK_WSU

    I wonder if this was a brand new rifle or if it had been used a bit before the torture testing.

    That would be a very cool job in my opinion. Get paid to break stuff.

  • Maigo

    DI or Piston, those barrels are dead and aren’t hitting anything anyway

  • Jim

    I’m bothered by how unscientific and dangerous this looks. Couldn’t they figure out a way to do it from behind plexiglass or otherwise just rig up a massive 1000 round mag that would feed it till it exploded?

  • Whatever

    Even though what was shown was very atypical use, would a slightly reduced rate of fire help with reliability? Or do the end-users of the M4 like the high ROF for short bursts?

    I wonder if simply scaling up all the components a bit would also help with reliability. It would add weight but IMHO the pursuit of cutting weight from a service firearm shouldn’t be the primary goal. Personally I’d rather have a firearm that weighed a pound or two more if that firearm was more reliable.

  • How do you actually set up a test like that? How do you keep feeding it rounds? Are the rounds spaced out equally? Are they as fast as the weapon will shoot? Those are just a few factors that I think need to be looked at.

  • jdun1911

    You don’t need to be a PH.d to understand piston will get hotter then DI.

    It is a fact that DI BLOT will be hotter then piston because the supper heated gas will be hitting it from behind.

    Heat does not magically disappear because there is a piston. The heat is still there just at another place, ie the piston face. Piston guns will get hotter then DI guns because it generate friction heat by the piston moving back and forth.

    Here is an AK-47 that’s on fire and it has a much wider gas tube then an AR15 piston.

  • Whatever

    “Piston guns will get hotter then DI guns because it generate friction heat by the piston moving back and forth.”

    Not likely. The piston in a long stroke rifle like the AK isn’t rubbing against anything for most of the time. And the piston face isn’t seeing the hot gas moving through it like what happens to the AR bolt and bolt carrier. More surface area means more heat transfer.

    That the end of the piston in a AK gets hot really isn’t a big deal since it’s nothing more than a hunk of metal. It has no moving parts within it, no extractor or firing pin to fail if they get too hot.

    If direct impingement was cooler running than long or short stroke piston actuation, then there would be general purpose machine guns (like the M60 or the M240) using direct impingement. To my knowledge there aren’t any.

    Everything has it’s pluses and minuses, the AR and the AK included. Neither is perfect as if either was, nothing else would be used.

  • Bill Lester


    That AK video doesn’t really document much. How many rounds were fired before it ignited? There are a bunch of 75-rd. drums already scattered at the shooter’s feet when the video begins. This pile is distinct from the magazines he uses in the video.

    Interestingly, the AK worked all the way to the end even with this kind of abuse. The guy gave up before the weapon did. It looks like his ammo supply was also nearly depleted.

  • Carl

    Simple solution: Remove the full auto mode.

    Other things you could try: make really big ventilation holes in the hand guard and make the gas tube thicker and possibly from a heat resistant alloy like Inconel if it isn’t already.

  • jdun1911

    The comments section pointed out that it was probably less then 700 rdns through the AK. It caught on fire on same region as the AR DI gun.
    The gas block is the hottest part of any auto rifle.

    You can’t denied that piston doesn’t generate extra heat by moving. To said that piston run cooler then DI guns is ridiculous.

  • Tom

    What is the barrel Dia. of the M4 and M4A1 under the handguards ?

  • Lance

    I agree with Jdun1911 look at it this way as well Charles E Kelly a WW2 hero won his C.M.H. with 2 BARs he shot his first one so many times it warped the Barrel and got too hot to touch nad almost the same to the second BAR. The BAR was ment to be shot on ful auto for long periods of time but even that had its limataions. The piston on them gets too hot to function. Same for a AK or M-1 the piston can only take so much punishment before amlfuntion and yes they happend to M-1s as well.

    Its a matter of useing the weapon beyound of whats its designed for its what as fault here.

  • Destroyer

    yes, even gas piston weapons do get hot. How can you use this excuse to justify the direct impingement design? gas piston designs keep most of the heat in the gas tube and behind the piston, away from where the bullets are fed and the action (which is where most of the malfunctions are caused). Direct impingement heats up the action and dries up the lubrication, which accelerates wear.

    Yes, this is a test that exceeds the purpose of the M4, though stress tests are invaluable to military arms.

  • Marsh

    It is a problem. Soldiers have complained about their M4s overheating and not working in firefights. When you’re stationed in a base in the middle of enemy territory and there’s only 12 of you and several hundred of the enemy you have to shoot a lot and quickly. Not all soldiers can maintain shot per minute discipline in order to prevent their guns from overheating. Heavy barrels are a must. They’re more accurate too. The military needs to force Colt to update their design and put heavy thick barrels on their guns. Going to a piston system as well is debateable but I’d rather have a piston gun because they’re easier to maintain and while the may not be magnitudes more reliable they’re still more reliable on average. It’s worth the extra weight and slightly slower target presentation as far as I’m concerned.

  • Lance

    @ Marsh

    The Army is doing just what you were telling us the Army should do. The marines are looking into the HK 416 for ther IAR many think its a way to adopt the 416 period.

  • Tom

    Heavy barrels are better.. I would like to see this same test done with Colt`s piston system.. or other piston system`s out there.. That would answer every ones question`s..

  • Destroyer

    i don’t have any problem with the HK 416 and believe it would serve the military fine, though i disagree with adopting another 5.56mm rifle. Perhaps a M4 with a heavier barrel, gas piston design, and 6.5 grendel upper would serve the military better.

  • Redchrome

    For those who want an empirical comparison between DI and piston designs, read the article here:


    A full-auto m4gery lasted 264 rounds on full auto (feeding from C-mags) before the gas tube burst. Bolt face got to 133F after only 264 rounds.

    A piston gun went 1036 rounds with the only problems being a bad magazine. Bolt face got to 122F at the end of all that.

    They did note that the DI gun’s gas block was cooler; reaching 339F. The piston gun’s block reached 697F. The more massive gas block on the piston gun took longer to dissipate heat.

    That said, a burst gas tube is a deadlined AR. It’s not a binary failure either… As witnessed by the difference between 264 rounds to failure with one gun, and 911 rounds with another, and the failure progressively getting worse along that time; gas tube failures are dependent on rate of fire, lifetime heat cycles, storage & cleaning conditions, and other environmental factors. Sometimes they last a long time. Sometimes they don’t. In any case, there seems to be some pretty firm evidence that piston guns are more reliable.

  • Tom

    I`d like to see gas tubes made of High Temp Alloy`s

  • Tom

    of all the gas tubes out there.. who use`s a better quality high temp metal ? i have never seen this discussed before

  • Lance

    I like your idea Tom ive never thought of that before.

  • Destroyer

    high temp alloy or not, the DI design still heats up the bolt and chamber, drying up the lubrication, increasing friction between the bolt and bolt carrier, and increasing wear on parts because of lack of lubrication. This video is further evidence damning direct impingement designs.

  • Lance

    Destroyer you seem fixed on attacking a AR when ever it appears on this site. I know many have differnt opions on ARs but good greef every one has moved on past M-4 debate since the Pentagon has asked a M-4 upgrade.

  • Destroyer

    lance, obviously not everyone has moved on. People on various posts (im not going to name names) are still fixated on the direct impingement design by looking at ways to improve them when it is a obsolete design. You also completely missed my previous posts supporting whatever design works the best (the fact is that the DI design doesn’t work as well as other technology). As i previously said, my posts grind gears with AR15 fanboys but could care less. My intention is for the military to be equipped with the best rifle in the world to suit soldier’s needs. The truth hurts, doesn’t it?

    • Personally I think whatever works. The gas pistons on AR-15 have their own set of problems such as carrier tilt. I think anybody is going to design a new gas piston system, but the issue is should the AR-15 use a piston.

      I used to be pro-piston, now I am neutral (with regards to the AR-15/M4/M16).

      I am sure the DoD will make the worse decision possible 😉

  • Carl

    It’s worth keeping in mind that there are other reloading mechanisms available. Blowback (Cetme/HK G3) and recoil (Barret M82) for instance. Designers of new weapons should not get fixated on just DI or piston.

  • Destroyer

    “I am sure the DoD will make the worse decision possible”

    indeed they will, history is on the side of that fact. I agree with carl and have put much thought into it. Technically you should be able to make a recoil or blowback operated assault rifle. Whatever works i guess

  • Lance

    I personaly dont care and will support either going to piston or staying with DI. Ive shot both and both shoot good. What ever AR system the Army wants im sure solders will countinue to enjoy the fine layout of the M-4.

  • ERIC 1/75


  • Does this Level IV plate (http://www.engardebodyarmor.com/hardarmor.htm#aramid) stop M4 and M4A1 bursts?