Polymer AR Lower Exploded

Nathan Brown posted this up.

Carnage of a polymer lower AR exploding!!! 8ft blast radius of pieces!!! Lucky no one got seriously hurt!!

I have not seen damage to a BCG like this before.

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Below you can see the bottom of the carrier sticking down at an awkward angle.


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Below is what was recovered from the last round fired.



It is truly a miracle that no one was harmed when this exploded. I cannot tell which make of polymer lower this was. I wonder how much destruction would have happened if it had been a forged or billet lower?

Nicholas C

Co-Founder of KRISSTALK forums, an owner’s support group and all things KRISS Vector related. Nick found his passion through competitive shooting while living in NY. He participates in USPSA and 3Gun. He loves all things that shoots and flashlights. Really really bright flashlights.

Any questions please email him at nicholas.c@staff.thefirearmblog.com


  • Ad

    I cannot imagine a polymer lower failing like this with normal use, but what i can essily imagine is that a polymer lower will explode more spectacularly than a forged lower when a KB occurs, which kinda looks to me is what happened here.

    That said, the smaller fragments and lower weight of polymer makes any fragments that do come off a lot less harmful than half a forged lower tearing off and slapping you in the face, but there’s a higher chance of getting one in your eye as a result of there being more of them. It’s a roll of the dice in the end. Always wear eyepro.

    • Twilight sparkle

      Also the material differences that cause polymer to blow up more spectacularly than aluminum could also help divert the blast away from your face. All the pressure looked like it went down away from the upper to the weaker lower instead of the upper blowing up in the face of the shooter.

      • pun&gun

        That usually happens with any firearm, AFAIK. Just blasts out the magwell and usually shreds the magazine in the process.

        • BryanS

          Another reason to keep your hands off the magazine while shooting.

          • Larry Lawless

            Buy a name brand lower you trust, not just the least expensive. Better yet don’t buy an AR, they are crap.

    • Just say’n

      Yup, another Click Bait Headline on TFB. KB had nothing to do with the polymer lower.

      • Sunshine_Shooter

        This isn’t much of a click bait headline. Headline is poly lower exploded and we have a poly lower that was exploded. Did the headline change between our comments?

        • ExMachina1

          Agree. This headline is about as matter of fact as you could make it.

          • Norm Glitz

            Not really. The blowup happened in the chamber. The bolt & carrier were blown out and down into whatever lower was there. That this one was polymer is completely irrelevant.

          • ExMachina1

            “That this one was polymer is completely irrelevant.”

            Have you seen photos of KB-ed aluminum receivers?–show me a photo of one that fragmented like this one did. Seeing how polymer ARs lowers respond differently to KBs seems very relevant.

          • clay

            What does the fragmentation have to do with anything? Hell fragmenting bullets are less dangerous in certain conditions.

          • nadnerbus

            Everyone knows a kaboom happens in the upper, and to my knowledge, there are no polymer uppers. The point of the title was to convey this kaboom took place on a polymer lower, since that is less common and may be of interest, while not using a title 20 words long.

          • Stephen Paraski

            Original Carbon 15 rifle had a non-alloy upper. Has any one ever heard or seen one of those explode? They were produced by Bushmaster. A friend picked one up 3 years ago brand new, never fired in box for under $500.

          • Core

            They are very durable. Bushy made sure the carbon poly was very strong. I’ve heard of early production flaws but never a case of blowout or weakness. That said any upper can explode if you use faulty cartridges, bolt carrier group, or poorly headspaced barrel extension.

          • rick0857

            To the best of my knowledge NO FIREARM leaves ANY manufacturers facility WITHOUT being TEST FIRED…So to say your friend got a new in the box NEVER FIRED gun is at least suspect.

          • Larry Lawless

            at least three rounds to assure it fires and chambers and ejects

          • jonp

            I’ve got 4 if them. I’ve put a few thousand rounds down one and several hundred down the others with no sign of fatigue or any problem. My wife likes them because they are lighter

          • Tinkerer

            20 words long? Need only add 3: “after case failure”.

          • Core

            Well put.

          • M40

            I would just change “exploded” to “destroyed”. Big difference between these two terms. One implies that it somehow self-destructed, while the other (correctly) implies an outside force.

          • Larry

            Check again, there are polymer uppers available theses days

          • Charles Springhorn

            My Bushmaster Carbon-15 has a polymer upper & lower

          • Larry Lawless

            The blast force went back to the point of least resistance, the receiver………………..

        • Tinkerer

          The title is misleading about the origin of the explosion. By not mentioning that the explosion’ s point of origin was the metallic upper receiver, it implies that the polymer lower exploded all by itself.

          • Dan

            No the title is not misleading. How or why would it blow up in the lower? A round going off in the magazine? If what you got out of the title was that a lower just went boom all by itself then it isn’t the title that has a problem.

          • Core

            There could be some assumption by those who do not know the fundamental principles of the Stoner platform. Leading some to believe that the lower had something to do with the bang..

          • Andrew


        • Muaddib

          Because the lower didnt explode?

          The upper blew out and the sidewall on the lower broke off, seen images of aluminium lowers doing the same thing on this very site.

        • Stijn Van Damn

          No that is bullshit, the lower did not explode, something catastrophical happened in the upper and it shredded the lower. If it had been an alu lower, Would anybody have been saying that the magazine exploded? no.

          The lower did not “explode” on it’s own.

          • clay

            Key words are the “lower did not explode”. The lower was destroyed by the explosion

          • Larry Lawless

            Duh !

        • Andrew

          They could have just as well said that “bolt carrier” explodes. Or “upper explodes”… Give us all a break.

          • BraveNewWhirled

            Guaranteed: Somebody would find fault with that as well.

          • Larry Lawless

            civilian AR’s shoot 55 grain, not a hot load.

          • Andrew


        • Mikial

          I have to agree with the “click bait” line. When I saw the title my first thought was “Oh, a polymer lower failed.” That was not the case at all. Something catastrophic happened in the upper. All you have to do is look at the carrier to see the problem started there. I’m certainly not an expert, but I would start bu investigating the possibility of an overcharged hand load.

        • Leadsled

          The only thing that explodes is ammunition. Again, dead silence on the type of ammo used.

          • Larry Lawless

            commercial 55 grain ???

      • bobby_b

        How bored and lonely do you have to be to keep visiting a site that obviously bothers you so?

      • BryanS

        No one said, not even in the title, that the polymer lower was the cause. It was, an explosion….. a Kaboom if you will… in a rifle with a poly lower. While there are lots of pictures of failures out there in poly lowers that are minor wear, this is a first that I have seen published.

        • clay

          The title clearly states that the lower exploded. That is false, the lower was destroyed BY the explosion.

          • Andrew

            “I cannot tell which make of polymer lower this was.”

            and you shouldn’t because it wasn’t the fault of the lower.

      • I’m O.K. with the title. It said the polymer lower “exploded” and sure enough it did. I never once thought it was the lower’s fault, just that it happened.

        I own a polymer lower, so for me this is educational as to what could happen. It helps others decide if the polymer route is worth the potential added risk.

        • Aaron

          Hey Aaron, it’s another Aaron. One that handily comes with a Materials Chemistry degree. Polymers are actually stronger than aluminum, so there isn’t an additional risk. Any KB is going to be really catastrophic, and flying shards of plastic will be less dense than metal, and cause less injury. It looks like someone used a severely overpressurized round then capitalized on the public’s misunderstanding of “plastic”.

          • BrotherLazarus

            It’s kind of funny, they’ll trust an SUV that’s some 60% polymers and fiberglass, but you slap it in a firearm and suddenly “BUT BUT IT WILL EXPLOOOOOOODE!” while showing off the same four or five ancient Glock stories.

            I’d make a joke about “new means bad!”, but I still carry a 1911 and my potential update is moving a whopping 30 years into the future and picking up a Hi-Power so I don’t have a lot of room to speak; outside of my old Glock 22 never exploding, deforming, or otherwise misbehaving.

          • Aaron

            Yeah, I personally don’t care what weapon I use, I use them as tools, so I look for efficiency. Light weight, reliable, gets the job done. Glock, XD, ect fit the bill the closest. I like 1911s too, any gun really. It’s just when it comes down to it, I’d trust a 1911 of course, but I’d rather have twice the magazine capacity and half the weight, personally. I can also break it down, clean it, and then go eat breakfast while my 1911 friends are still working on theirs.

            For the accuracy, there are millions of videos on youtube of Glock 100+ meter shots, that’s more than enough for me for sidearms.

            As to the vehicle analogy, I remember being at a car show with a friend, and some guy was talking about how the classics were better cars than the ones today. I mentioned that today’s cars were far more reliable and safe than they have ever been. Most of my vehicles though were mid 80’s beaters I paid a grand for and drove them until they died, then scrapped them. I always saw a car as an appliance, like a washing machine. Cheap as they were, they lasted forever with no major issues. My last one was a 1989 Tuarus wagon with 280k miles on it when it died, after 7 years of reliable service. Never had a breakdown, never failed to start. I wrecked it, then drove it for 2 more months before it finally stopped working.

          • BrotherLazarus

            I have a bit of a hate-on for Kimber and newer-era Colts for ruining the reputation for reliability that Browning designs carried–they didn’t carry that rep because they locked up tight and were precise carbine-range shooters, they carried the reputation because you shake a 1911 made to original specs and it sounds like a rattle–you can almost lose a small dog in the lockwork without malfunctions. You can still make ’em pretty, sure, but trying to tighten everything up to the point where a little dirt or sand starts causing issues is kinda like gold-plating an AK-47–the person doing it is entirely missing the intended point of the design.

            Then again, I still near have aneurysms explaining to people that most handgun ammo specs printed by major manufacturers are fired from ten to twelve inch test barrels, so they’re going to lose velocity out of a four inch bbl carry piece.

            Some folks just attach too much meaning to a label, a brand, or a particular structural material.

          • Larry Lawless

            would you drive a truck with a polymer front end or drive axle ?

          • BrotherLazarus

            One, most people already drive trucks with polymer or fiberglass front ends. Two, depending on the polymer, I probably wouldn’t balk at a poly drive shaft.

            Polymer does not equal basic plastic. There are a number of polymers that are as strong as steel, both in tensile and shear (“shear” as in sliding failure akin to tearing, not “sheer” as in overall) strength–and certainly stronger than aluminum, which a large number of modern firearms are made from these days.

            Usually my response is “would you shoot a gun made out of a soda can?” at this point, because it’s about as relevant and valid a comparison as thinking of polymers in terms of tupperware–that is, they’re both irrelevant and invalid comparisons.

          • Very good to know Aaron. I had heard contrary information (obviously from the metal purists who believe metal is better), that the polymer receivers were weaker and therefore more prone to failures (cracks, breaks). I heard polymers were just as good and lighter, which is why I bought one. So far I’ve been very happy with my polymer receiver, but I still had lingering questions.

            I do have a follow-up question for your expertise. In a catastrophic failure like this one, will the metal receivers tear/split more with less pieces of shrapnel? The polymer one above looks like its in quite a few pieces, where some of the metal ones I’ve seen have more tears/cracks. Is that a difference between metal bonding and polymer bonding?

          • Aaron

            Well, I think we can agree that any lower will be destroyed when something like this happens. I think with an explosion like this, there will always be shrapnel, and that will vary depending on how bad it is, of course.

            Plastic can usually stretch more than metals. The bonding is different, metals have single atoms bound to each other in a lattice, polymers are large molecular chains.

            Like I mentioned, with a KB, I think polymer would be safer, as the fragments are too light to penetrate deeply, and would also most likely be stopped by safety glasses.

            But I’ve never had a KB in all my years of shooting hundreds of thousands of rounds. That is more preventive maintenance, watching what you shoot, ect. They are like airplane crashes, rare but sensational when it happens.

            Polymer or metal, if the lower is engineered correctly, it won’t break under normal wear and tear, and being dropped, ect. The only thing I wouldn’t recommend them for possibly is if you are in extreme cold environments, as I mentioned to another poster here, most all plastics get brittle in extreme cold temperatures, metals as well, but that is much lower.

          • Great info! Thanks Aaron.

    • clay

      The lower DIDN’T fail.

      • M40

        Umm… it didn’t exactly succeed either.

        • mbrd


    • Fabian

      What’s a KB?

      • evguy2

        KB = kaBOOM.

        This was the result of a badly overcharged cartridge. That poly-lower is an innocent bystander.. click bait title.. bad article..

        • Fabian

          Thanks, this explains it.

        • BraveNewWhirled

          Everything these days is clickbait, fake news, and/or racist.

    • Larry Lawless


  • jrt 82

    Not a lower issue, its a “fired out of battery” issue.

    • ExMachina1

      The notion of out of battery firing in the AR is an old wives tail that will (apparently) never die. You can google it for yourself, but there are many reasons why OOB firing should be impossible in the AR.

      • Sunshine_Shooter

        “should be impossible”

        • ExMachina1

          I’m happy to be persuaded but the evidence for OOB in the AR is simply not there. Take a look at the primer above and it exhibits every sign of an over-charged case…

  • FredXDerf

    !!!Breaking news!!! Water is wet !

  • Pedro .Persson

    Bulged and cracked upper as well, the whole gun is done… can’t really blame in on the lower, can you?

    • Dan

      No one is blaming the lower. It is just showing the result of the kaboom with a gun that had a polymer lower. That is all. Seriously that is all this is.

      • L. Roger Rich

        Fake News so common now days,

  • Spencerhut

    Nothing to do with the poly lower, that was just a plain old kaboom. My wife had a squib in a Hi-Speed class with a line full of shooters that did about the same thing to her ~$2500 metal AR. Blame the ammo, not the gun.

  • wheynoWade

    Why the .22 lr brass in the pic?

    • Phillip Cooper

      …because it’s at a shooting range???

  • Ryfyle

    I’m wondering what brand of rounds were they using. The Level of destruction indicates that not a lot of metal lowers would have stood much of a chance either. This dose make on think how a welded lower would preform.

  • HansonBro

    It just exploded out of thin air.

    Cause – Magic pressures.

    Good lord, how stupid do they think we are?

  • Tinkerer

    Clickbait title is clickbait.

    • Dan

      Why? An AR with a polymer lower went boom. I see pictures of a gun with a polymer lower that went boom. What exactly were you expecting to see that was not shown?

      • Tinkerer

        It’s a matter of causality. The title is written to imply that the origin of the explosion was the polymer lower itself, when in reality it was the failure of the metal bits housed in the aluminum upper.

        • Dan

          No it isn’t it was written to say hey we got this her plastic lower looked what happened when the rifle went boom. And then the author asks what an aluminum lower would look like in the same situation. Nothing misleading about this. I certainly did not think oh hey a polymer lower that just decided it was made of C4 and blew up on it’s own. You people look for something to complain about and find it in the dumbest places.

          • MichaelZWilliamson

            “Polymer AR Lower Exploded After Chamber Failure” would be less clickbaity.

  • Mike

    The face on the buffer looks pretty hammered, I suspect this rifle has been used and abused. Rode hard and put away wet and dirty.

  • USMC03Vet

    Nothing of value lost.

    • ExMachina1

      Sadly, that hand guard can probalby be salvaged…

    • TheNotoriousIUD

      He could put it in the garage and hang water hoses and extension cords off of it.

      • DanGoodShot

        Or use it as it was originally intended… shelving.

    • MichaelZWilliamson

      Yeah, rails can at least be used as a good cheese grater.

  • Sianmink

    .300 in a .556?

    • Mystick


      • BryanS

        .300 in a .556 might be interesting too

    • Kivaari

      Looks like Wolf steel cased 5.56mm.

  • Drew Coleman

    The material of the lower is not in any way relevant to failure. This was an ammunition failure or an OOB detonation. No lower would have come through this unscathed.

    • ExMachina1

      I believe the material of the lower might affect the manner in which the lower failed. The kaBooms I’ve seen on aluminum lowers were not as fragment-y as this. IMO, this is a good data point to keep in mind…

      • Aaron

        I’ll give my input as a chemist, specifically in materials, which I feel is relevant. Most polymers are actually stronger than steel and aluminum. This was a case of a KB, and not a failure of the lower itself, as was obvious to everyone here. Polymers are less dense than metals, and would cause less injury as fragments, assuming user is wearing proper protection, of course.

        This article looks to be something sensational meant to scare an ignorant public about “plastic” parts. Most people don’t realize many polymers, Glock frames and such, are actually stronger than metal frames.

        I’ve found many articles on this blog to be frankly wrong, and written by people that do not know much about firearms.

        • NoDakNative

          Stronger than steel and aluminum by what metric? Weight? Density? Rather important details for a chemist to be leaving out. I bet you know that wood is stronger than steel, but that is worthless if you don’t say by what metric. In that case, it is by weight.

          The problem with polymers, as used in guns, is that they tend to be more brittle than metal. (Not all polymers are brittle of course, some are quite flexible.) Depending on the design, this is designed around with metal reinforcements. While some failed metal AR lowers, that I have seen online, have fragmented like the polymer one here, most have held together and sent the gasses down out the magazine well.

          Personally, I would not buy a polymer lower because of the climate I live in. I have accidentally shattered P-mags at -20F before and it is an inconvenience. Shattering a lower is a much bigger deal. So even if the chance is remote, I’ll take the material that I know handles cold better.

          The problem is not the article. The problem appears to be an infestation of people who lack common sense and require 25 word titles. AR-Kabooms on Aluminum lowers are common to find. What happens when one happens to a polymer lower are not. I immediately figured that it was some sort of KaB by the title.

          • Aaron

            Tensile or deformation strength, mostly. I left the details out because unless you are familiar with nuclear physics, calculus 3, or linear algebra, you wouldn’t understand. I don’t mean this in an elitist or “I’m better than you” sense at all.

            Polymers are brittle, to an extent. But there are resins called plasticisers that are used in the formation, polymers are a mix of multiple chemical plastics, based on what parameters you want. Thus, some plastics end up more or less brittle, stronger or more flexible, depending on which ratio of different polymer compounds are used. Graphene tubes and nanopolymers are still in research, but promise much stronger and lighter plastics in the future.

            It’s incredibly fascinating. I went to college on the GI Bill, did a tour in Iraq in 2004 as a combat medic, was always interested in the sciences. I dropped out with 2 classes remaining to my degree because of PTSD, I’ve dropped out of college 5 times already. I moved to Washington state, and smoke legal weed, which is much better than all the pills the VA has given me the last 12 years.

            Anyways, back to the subject at hand.

            I completely agree with your low temperature assessment. Low temperatures have always been a problem with polymers, the ultralong molecular chains that give them their strength and lightweight, are a burden with temperatures, and the plasticizers are less functional there. But, the lower would be fine, I think, even there. Magazines are made of a more brittle and thinner material, which is a necessity, no one wants a magazine that costs $150 apiece for the fine tuned right blend of plastics.

            I agree, a KB was my immediate assessment as well. The blame was placed on the material in question as a scare tactic like the “tupperware” Glock thing a couple decades ago.

            I understand with the polymer lower thing, each gun owner must understand the parameters that their weapons will function with. After all, you are the only person that will pay if your weapon choices end up in error.

  • Shane Tomlinson

    One of my buddies had a failure like this several years ago. We’ve tried to pinpoint the root cause sense then. The use of after market parts and reloads make it difficult but I believe that the issue came from the bcg. my buddies gun was built for 3 gun competitions and he had a lot of high end parts on it. The tolerances for these “add on” are not always mil spec and often not observed or even remembered after the purchase. He had a high end titanium bcg that, after reseaching, only had a 3000 round life expectancy. He competed quite often and practiced like crazy. As a result he exceeded the expected life tolerance and the lower exploded. He had to get a chunk of titanium removed from his belly…..his bolt looks a lot like the one in the pics above.
    My guess is that this AR was a budget build and may have had a low quality BCG that obviously failed in the same way that my buddies failed. Makes you think about quality.
    Buy quality cry once….. the cost will make u cry
    Buy cheap cry twice – when u buy and when it fails.

    • Norm Glitz

      “Dimensions” not “tolerances”.

      • Shane Tomlinson

        No tolerances. We’re not talking about size …. it’s about the expected life of the parts. In this aspect I’m talking about “the permissible deviation from a specified value”.
        Someone also mentioned that it could have been a 300 BO round .. that’s a possibility as well.

  • Matt Frikin Bennett

    You should really clarify that this is in no way the fault of the lower receiver.

    • Dan

      You should really clarify how anyone is blaming the lower? Where does it say that? Oh wait it doesn’t. Not the authors fault people jump to conclusions.

      • MichaelZWilliamson

        “Polymer AR Lower Exploded”

        Strongly implies the lower failed in some fashion.

        It’s like saying, “Man hits steering wheel!” when what happened is he wrecked while not wearing a seatbelt.

        “Polymer AR Lower Exploded After Chamber Failure” would be less clickbaity.

        • M40

          Kinda like running an article titled, “Chevy Trucks Explode”, and then you read it to find that they are showing trucks in Afghanistan that hit IED’s. The trucks didn’t “explode”, the IED’s did.

          There’s a rather big difference between something exploding and something getting blown up.

  • TheNotoriousIUD

    Maybe it was haunted…

  • Mystick

    Probably a “non-5.56” upper used on a “5.56-marked” lower and yet again the incorrect ammunition was used. I’m sorry, it’s just one of those thing that rubs me wrong.

    • Rick O’Shay


      • MichaelZWilliamson

        .223 Chambers are tighter spec than 5.56. It’s rarely a problem but can be. The lower is not relevant, though.

  • spotr

    The flash hole looks very large. Its almost as large as the primer cup area. It might be due to the ka-boom, but maybe also due to a reloading issue. If the de-primer tool is pushed too far into the cartridge, it enlarges the flash hole. Here is a side-by-side view of a normal 5.56 cut-away https://uploads.disquscdn.com/images/d3641cf5d9fe3e1c93588f52a46c46ed30bf0d2f0d36acc4bb1c1502e8e0953b.png which I tried to scale to the same size as the picture.

    • TechnoTriticale

      Excellent observation. That flash hole diam needs some ‘splainin.

      Do we even know if the kaboom happened on bolt close or trigger pull?

      A photo of the chamber would have been useful here, not to mention a legible shot of the headstamp, and some word on whether the barrel is still clear, or has, say, an oversize projectile stuck in it.

      The polymer lower is most likely an innocent bystander.

      • Political Smackdown

        i tend to agree the lower simply could not take the shock

    • mig1nc

      Thank you for posting that. It’s pretty interesting.

    • Vicki Hampton

      I was also wondering what type of primers were being used? military or bench rifle/target

    • kivaari

      Was the flash hole large before or after the cartridge was fired?

      • MichaelZWilliamson

        Are you suggesting the shooter was a flashhole? 😉

        • Cole Johnson


    • Political Smackdown

      if you undercharge the round you can get a primer flash over the top of the powder causing detonation … or he could have simply stuck a 300 black in the mag.

      • mazkact

        .300 Blackout………………….that.

    • Tritro29

      On the money.

    • glenn cheney

      Glad I read far enough to hit your post. As soon as I saw the blown out casing, and if you enlarge the pic, I can see what might be flash burn beginning to creep thru just adjacent to the cartridge casing blowout.
      The source of this failure goes to that primer and casing.
      Don’t know the ammo mfg, or if reloads, but in my humble bumble, I think the expert ATF dudes eo t king exposes would go with your assessment, I do.

      • Wolf

        And squib stuck in barrel when second round fired. ??

    • Ron Smith

      “If the de-primer tool is pushed too far into the cartridge, it enlarges the flash hole.”

      Ummmmmmmmm, bullshit. No depriming tool on the market for at least the last 30 years will enlarge a flash hole by being “pushed too far in”, the tool will bottom out on the case and then you bend the decapping rod. Not even the flash hole deburring tools will do that, they all have designed in stops. You would have deliberately drill a larger hole for it to happen during the reloading process.

      I have seen that happen to flash holes from gross overloads that took the gun apart. All the signs on the remains of the case and the damage to the gun point to one of several possibilities: 1- .300blk in a .223 or 6.5 grendel chamber. 2- 6.5 grendel in a .223 chamber. 3- gross over load of a way too fast powder. 4- being a totally unaware twit and firing a squib or three to clog the barrel then a full power load.

    • BraveNewWhirled

      Nice work. Happy new year.

  • ExMachina1

    Primer tells the tale–overcharged case. That degree of primer flow is extreme

    TFB should not tag this as “out of battery detonation” since that is highly speculative. OOB firing in the AR is not a phenomena that I can find any credible source for, and is theoretically impossible in the AR design

  • Ark

    As is their wont.

    A good aluminum lower is like $40. There’s no reason in the world to get a plastic one.

    • Random Disable Person

      Maybe because during the great firearm panic of “(November 2008-ish)/ January 20, 2009 – to January 20, 2017( November 2016-ish)” people were forced to buy the polymer lowers, if they couldn’t get a metal receiver? Some were lured by the price difference, some wanted to try a new design/type. Some wanted to build their own lower…
      Some were decived by adverts by companies withholding the fact the lower receiver was polymer. Those bottom dwelling retailers with their “no returns/no refunds” or they charge absurd restocking fees, after the non refundable profiteering in shipping and handling… Basically to make sure people don’t ask to get a refund, since they will only get a small amount of their money back for a product that was misrepresented. Because the buyer will have nothing for the money lost and hassle. If they returned it under those terms, where they just about(or did) buy the item for the company and gave them profit to accept it back to resell with no incurred cost of the item making the next sale 100%+ in profit. YMMV with completed poly-___ AR-15 lowers & complete rifle sellers, I have seen very few honest ones that point out the lower was not milspec metal.

      Hopefully metal receivers will stay available in bulk and stay at the affordable prices for the lowly common masses. That is the one true gift we have from the panic. Company’s invested in upgrading their production lines for demands and now can & do produce more products which allows better bulk material cost savings. More sales lead to upgrading equipment and systems able to churn out more product per hour. New companies(already established in other machining work) entered the market due to volume. Starting a good feedback loop for both sides.

      On the kaboom, I’m surprised the receiver extension didn’t also split and break off , since they are notorious as being a weak point in polymer lower receivers. Maybe some one should ask the BATFE about the third hole the firearm now has 😉

    • Cymond

      Weight, for those who care about such things.

      My first compete lower was a New Frontier because I was new to the AR-15, and it cost less than the parts to complete the stripped aluminum lower that I had. Today that polymer lower serves as my dedicated 22lr lower, and the light weight is nice.

    • Aaron

      Other than “plastic” being stronger and lighter than aluminum, of course.

    • MichaelZWilliamson

      Other than the plastic not being the cause of failure and the aluminum upper is deformed enough to be useless as well.

  • A.WChuck

    “Imma load me some hot rounds! (drives to range later that day) Kaboom! “Dang ol’ polymer lower!”

    This has been another episode of “Shift the Blame Theater”

  • Tacos4Breakfast

    I’ve seen this a few times and in EVERY instance it was someone trying to fire a 300BLK out of a 5.56/.223.

    • VeteranGunsmith at large

      Roger that. Definitely overpressure in the breech without the bolt fully locked. I saw this same kind of failure a few times on M16 rifles in the Army (pre A1 version) because someone used the FA to close the bolt when the previous round stuck in the chamber and tore the case head off during extraction/ejection, which is why the FA is a bad idea. If you can’t get the bolt closed – don’t jam it and then pull the trigger!
      The same kind of problem occurs when you chamber a round that exceeds chamber dimensions either slightly larger diameter, different shoulder profile on the case or excess length from the case head to where the ogive meets the rifling lead edge.
      I saw a Mini 14 destroyed by a guy who decide to fill the case on his reloaded 5.56 NATO caliber rounds. First shot blew the sides out of the receiver and the stock was obliterated. His reloads were not only much to heavy charged but the bullets were seated on top of the powder which made them too long to properly chamber. It is quite possible for the hammer to drop on an out of battery round in the Mini because the action is designed after the .30 M1 Carbine and the Garand family which all allow the hammer to fall when slightly out of battery. Probably one of the reasons that the M1 family was obsoleted, but the ordnance board will never admit it.

      • TechnoTriticale

        re: I saw this same kind of failure a few times on M16 rifles in the Army
        (pre A1 version) because someone used the FA to close the bolt when…

        The original AR-15 (including Colt civil SP1), XM16 and M16 didn’t have an FA. That feature appears to have come in with the XM16E1 and M16A1, so a “pre A1” wouldn’t have an FA unless I misunderstand the history.

        But sure, the FA is both a benefit and a hazard. I’ll bet, for example, that the 300BLK in 556 scenario involves an FA bump more often than not (and we can’t rule that out in this case based on the evidence so far presented).

      • VT Patriot

        Thanx for your expertise and real world knowledge. Quite informative.

  • Chris Cook

    Its not the damn lower that failed! It was an out of battery or breach lock failure. You can clearly see this in the pictures of the bolt, upper receiver and casing rear. Polymer lowers are the tip of the market and have been ridiculed for breaks even when it was not the problem because they are thought to be weak. 99.9% it is another component that caused the lower to fail or the assembly of crap parts or a crap builder. Even though that is the case the polymer lower is ridiculed.

    • Aaron

      Chemist here, the irony is polymer is stronger than both aluminum and steel. This is an article meant to scare the ignorant public. I’ve seen the same crap used with Glocks vs metal frame pistols.

  • inchang

    Doesn’t look like an issue with the polymer lower. The most catastrophic part is the upper which is all bulged and the bolt carrier is shredded.
    If a polymer lower snaps, then it just snaps. If the upper explodes, then there’s obviously something wrong with either the ammo or the upper itself.

  • KoyoteTan

    How is this a story about the lower failing? You clearly have the remnants of some kind of case head separation or out of battery discharge that would have little to do with the lower material. There are plenty of photos out there of similarly destroyed aluminum uppers and lowers from similar case head separations or out of battery discharges. The lower here appears to be a casualty of some failure that it did not cause. If this were some kind of a breakage around the rear or takedown pins or trigger pins then you could more easily finger the lower material as the cause, but an explosion coming from the chamber area of the upper certainly would not finger the lower as the cause.

  • Guest

    Think you used enough gunpowder there, Butch?



    • MichaelZWilliamson


      Also, the stock, grip and handguards tend to be polymer.

      Nor did the polymer have anything at all to do with this failure.

    • Aaron

      Polymer is stronger than steel and aluminum, actually. Don’t take my word as a chemist, though, research it yourself. You need to like math a lot, though, to understand any of it.

  • Political Smackdown

    clearly this was not the fault of the lower itself but the reality is it turned into Garbage. it should also be noted the magpul mag exploded as well. not a good thing at all the entire gun looks to be scrap the upper is cooked ant it is made of aluminum. notice how it held together tho? it cracked and bulged but did not turn into a shrapnel bomb.

  • Uniform223

    Now to make this comment section complete is an AK fanboy saying that this would never happen with an AK
    A comment by someone who has never shot an AR-15 but played allot of CoD

    • MichaelZWilliamson

      In fact, you can use ammo from the M60 in your AK because they’re both 7.62mm, and if you put an eraser behind the bolt it fires full auto. Also, the reason AKs aren’t as good here as in Russia is because Russia refuses to sell the secret Russian ammo that can shoot through tanks. In fact, an AK can be bent in half, buried in acid and welded shut and it will still fire.

  • Stephen Paraski

    A little JB Weld and that lower is good to go again.

  • Texas-Roll-Over

    This is what happens when you overcharge a load, or shove a 300BLK in a 556.

    I’ve seen BCG’s like this quite frequently with 300 BLK in 556 uppers.

  • Ed Forney

    Maybe a hand load with a double charge ?

    • MichaelZWilliamson

      Or overcharge, wrong propellant or damaged propellant.

  • Ed Forney

    I have two polymer lowers, never a problem.

  • Some Rabbit

    Lemme guess, another .300 Blackout fired in a 5.56mm chamber incident?

  • Chris Hunt

    Looks like a case separation issue with the ammo. Seen it before in a Bushmaster rifle. The lower didn’t blow apart but the upper and bolt carrier did. The rest of the ammo was blown out through the floor plate of the magazine. Even though the lower didn’t come apart in the KB, it was still damaged beyond ever being used again. Thus the entire rifle was a total loss and the only usable parts were the stock and forearm covers.

  • Louis Bethel

    Can anyone share further info on the ammo?

  • leewardboy

    Not a fan of most polymer lowers (though my CavArms lower is great) but in this case the lower doesn’t seem to be the cause of the problem.
    We had a 9mm AR go out of battery. A piece of the upper (aluminum) hit my friend in the back on the next bench over – he was shooting offhand. Required surgery – IIRC – did some damage to his spleen. Another friend had a OOB in an M1A – destroyed the receiver, mag, op-rod, stock and the bolt lost it’s right locking lug which apparently managed to hit the clip guide and severely deformed it. The heel of the receiver was cracked completely off – the bolt was hanging out the back of the receiver. He had pieces of brass and steel in his face and caught a few in his eyes – went in under his shooting glasses. Spent some unpleasant time watching the end of a metal pick as a doctor picked stuff out of his eyes. YMMV

  • L. Roger Rich

    It was not the poly lower that exploded. Probably a hand reloaded out of spec round exploded in the chamber.

  • N Man

    I’m impressed that both the safety detent and the rear take down pin detent didn’t get launched into outer space like the front one did..

  • RA

    Couple shots of WD-40, scrub with a toothbrush, and she’s good as new!

  • Greg Torchia

    It’s imperative to keep your bolt carrier group and Barrel extension lubed with grease not just oil on AR-15 especially during rapid fire most likely it was not a mechanical failure but bad ammo or primer discharge- I currently have polymer upper and lower AR 15 never seen anything quite like that

    • MichaelZWilliamson

      Odd. I’ve never used grease on mine in 35 years, including issue use of M16s, M16A1s, M16A2s, M16A3s, GUUs, GAU5Ps, M4s, M4A1s, and a couple of odd variants, about four dozen mfr civilian variations and some built on receivers I milled myself. I have 25 years of Expert ratings, several trophies. Where can I get this “imperative” grease I’ve been failing to use?

      I’ve just been following factory guidelines for 3-4 drops of oil, though I do accept the updated advice to lube heavily in the desert if there are problems with dust.

      • Aaron

        I used graphite lube overseas, never had issues and works better than oil in sandy environments.

        • MichaelZWilliamson

          My point is there are multiple lube options depending on environment, weapon specifics and usage.

      • Greg Torchia

        Gun grease works- for extended periods really well on my M1A Springfield I brought that idea over to use with my AR systems works good on Short Stroke Bushmaster 7 inch barrel professional Ordnance type polymer upper and lower- Short Stroke pistol metal to metal gets a lot hotter -especially under rapid-fire the oil loses its viscosity- where it simply evaporates- runs out or Burns off- obviously I wouldn’t use it anywhere in the lower the grease would attract dirt- the AR type design dust cover does keep most foreign objects out of the combustion chamber when used in conjunction with every use cleaning

  • Hunter

    I am new to Ar’s, how can I prevent this from happening to me

    • MichaelZWilliamson

      The lower didn’t “fail.” There was a chamber explosion, possibly due to bad ammo or mis-matched ammo. You’ll notice all the failure points were AWAY from the shooter’s face.

    • TechnoTriticale

      re: I am new to Ar’s, how can I prevent this from happening to me

      Well, we haven’t enough data to know what “this” is. Leading candidates are:
      ☠ 300BLK in .223/5.56 chamber
      ☠ barrel obstruction
      ☠ overcharged handload (factory defect ammo/case not impossible)
      ☠ out-of-battery discharge (hard to get on stock AR BCGs)
      ☠ and now for something, completely different
      ☯ any kaboom role for the lower is the least likely explanation

      To cover yourself, avoid all contact with 300BLK ammo, or develop really strict ammo sep discipline. If you handload, double-check for overcharges (or pick a powder that makes it all-but-impossible). Keep yer BCG clean and lubed. If you mod the AR, understand all possible novel malfunction risks that might arise.

  • brian

    Hate to tell ya…but if the metal in the bcg was deformed as badly as shown there’s no way in hell a forged or BILLET lower would have survived either! Nice attempt at trying to put a knock on polymer lowers though! Just about as bad as “fires 30 rounds in 3 seconds” and “ghost gun” nonsense. Portrayals like this do nothing for the gun community, as a whole, other than propping up “know it alls” in forums to talk more about junk they know nothing about. Me thinks the user should not fill a case all the way up with powder and then shove a projectile on top with a crimp….or prob not try to shove a golf ball through a garden hose with a 300 in a 556 barrel….this failure had nothing to do with “polymer” anything!

    • MichaelZWilliamson

      Well, it might have survived given the distance from the chamber, but the failure certainly isn’t due to the lower receiver.

  • Jason Bourgeois

    More info would have been useful. Round caliber? Handload or factory load? Did the caliber match the chamber? Was the shooter experienced or an amateur? Was it their first build? Was this the first time this firearm has been shot or has it had thousands of rounds through with no problem?

    Those bits of information can and should be shared preliminarily. I don’t expect the full forensic investigation of the firearm, but if you’re gonna take that much time to take that many pictures and post a blog about it, you could at the very least conduct a brief interview to ascertain the answers to those questions.

  • Wolf

    Podesta has just revealed proof of that the Russians did it.

  • Kelly Harbeson

    That looks like an out-of-battery discharge from the damage to the bolt and the recovered cartridge case. That’s generally pretty catastrophic whenever it happens.

  • Archie Montgomery

    Perhaps this is more a problem of ammunition than inherent strength of material?

    My thought is more information is needed. If nothing else, what ammunition was being used and for what round was the rifle chambered and proofed? Since the detonation seems to have occurred in the chamber, I’d like to know if a prior round left a bullet in the barrel, just far enough down bore to allow another round to chamber.

    At a guess, this probably would be solved by using non-detonating ammunition.

    As I recall, the Glock pistol frames tend to be more damaged with detonating ammunition as well. But they don’t seem to evidence many such problems with proper ammunition (and no bullets in the bore, of course.)

    • Aaron

      Polymer is actually stronger than steel and aluminum.

      • Archie Montgomery

        Ah. I’m not a structural engineer nor a metallurgist. However, from simple observation, polymer is strong enough to handle the stresses involved in the normal operation of a ‘container’ in this sense.

        I remember in High School learning that under tensile stress only, glass is stronger than steel in equal volume (thickness). So I’m not shocked at what you say. But I didn’t ‘know’ that before you posted this. Thanks.

        • Aaron

          I’m 2 classes away from my degree in Materials Chemistry. I have to take nuclear physics and inorganic chemistry, aqueous metals, to graduate. I did a tour in Iraq in 2004 as a combat medic, and used my GI Bill to attend school.

          My worsening PTSD symptoms have made me drop out and move to a legal state. The marijuana here helps me much more than all the drugs the VA gave me over the years.

          I’d like to go back and finish school once I am better, I want to pursue my masters, as ultralight super strong plastics are a passion of mine.

          • Archie Montgomery

            I can say only two things. YAHG!!! and I will be praying for you.

            I was in the Marine Corps during the Vietnam era. I was not on the ground there, but I was close enough. I seriously wish you well, Aaron. My own two cents is PTSD is fixed more by talking and learning to deal with it than drugs – which may take the edge off in the short run.

            God can fix it. He’s fixed me on several different accounts.

          • Aaron

            I consider it medication. I don’t do the whole “weed is cool” thing, and it was my last option.

            And time helps, some. Also, I do super long hikes during the summer, did the entire 2200 mile Appalachian Trail in 5 months in 2010, just hiking all day every day and living in the woods.

            I’m personally agnostic, I have nothing against religion, and really wish I could believe sometimes. It’s a long story, and very personal, so I won’t discuss it here other than to say it involved 18 years of brainwashing and a childhood almost as bad as my tour in Iraq.

            I really can’t complain, though. I enlisted early 2003, did basic at Benning in May-July, then medic school, unit assignment. Got to my unit and 2 weeks later we were flying to Kuwait. I knew what I was getting into signing up at that time and picking combat medic as my MOS.

            I grew up in TN, and was shooting from the time I could walk. I wanted to fight on the front lines, but didn’t want to watch people die and not be able to save them, so I chose medic. I can’t blame the aftermath, I knew what I signed up for.

          • Archie Montgomery

            And you were at your appointed place of duty. There’s lots of folks who won’t do that.

            Agnostic? That’s honest at the very least. And I’ll still be praying for you. At worst, I’m wasting my time.

  • Core

    This is bolt failure, which led to BCG failure, which blew out the polymer lower. The title of the article leads folks to assume that the lower was the cause. I’m guessing that the primer wasn’t seated or possibly it chambered a 300 into a 5.56?

  • Juan

    I agree with previous posters that the title is clickbait and sensationalist. With the damage to the BCG and upper, it’s clear that this catastrophic failure was due to dangerous ammunition, but the title makes it sound like the polymer lower just exploded from normal use.

  • Scott Lanier Sprayberry

    First and foremost, this carnage has nothing to do with the lower. The problem is way to much pressure.

  • Frank Hunter

    looks to me like the boom was in the metal upper not the poly lower, nothing went wrong in the lower and I believe a metal lower would have been just as damaged

  • BudHall

    I think most of us who have read and thought this through do see the truth. The polymer lower did not “Explode” as the title implies. It was damaged by an over pressure chamber explosion. And as several others have noted here, the flying polymer fragments may be less injurious than comparable alloy pieces. So if the author is biased against polymer, that’s his issue, not mine. I find it just a little bit insulting that we get fed this type of title line on this page. We don’t know that there wouldn’t have been some level of similar destruction of an alloy lower too.

  • clay

    Please explain how the lower has anything to do with the damage to the Bolt and carrier. Whatever the event was that created this Carnage was NOT related to that polymer lower. As much damage as that BCG took, the hard pieces from a forged lower would probably have been more dangerous.

  • David

    Without knowing the reason behind the failure, it is impossible and irresponsible to sit there and say the polymer lower was the cause.

  • MichaelZWilliamson

    So, what happened is some sort of chamber/bolt failure. The lower failing would have no bearing on this incident. It’s just a victim.

    We may as well say the receiver on my PPS43 “failed” when a squib blocked the bore and the next round blew down through the magazine, as designed, away from my face.

    And it appears this weapon also failed away from the shooter’s face. As designed.

  • Andrew

    This has nothing to do with the lower what so ever. Any lower would have been destroyed had this happened. It looks like an overload situation or an out of breach ignition. Either way the upper exploded into the lower. The title of this article is deceptive. Lowers don’t explode on there own. This is just an attempt to scare off folks from getting poly lowers. It’s silly to even suggest that this was a lower failure.

  • Steven L

    Sounds like the cartridge wasn’t fully chambered when it went bang. Then it is a crap shoot at where the cartridge failure occurs within the cartridge and the path the expanding gases take. Not sure what the outside temperature was but polymers all become brittle as the temperature drops and if this lower was 3d printed no telling if the thermoplastic used even contains a plasticizer. Meaning very brittle plastic at low temperatures. I’m curious as to whether it went bangduring the chamber chambering of the round or did it go bang when the trigger was pulled.

  • Andrew

    ITS PLASTIC! WTH do you expect?

    • Greg Kelemen

      Yeah I heard of this new company making plastic pistols called Glock? or something.. It’ll never catch on.

    • Spikey DaPikey

      Microwave safe?

  • Mickey Miller

    what I would like to know is if there is a 30cal bullet stuck in the barrel , because there is no info to the cause of the catastrophic failure . I personally would not admit to doing something stupid as putting a 300 blackout in a 5.56 rifle and pulling the trigger. and if that is what happened , physics took over and the “explosion” went exactly where expected . the weakest point , the polymer lower

  • tarnishedcopper

    The real question was what caused it, not metallic verses polymer. What allowed the weapon to fire out-of-battery, or could it have been cartridge prematurely detonating, or perhaps case failure? Earlier in the week there were photos on the net of a polymer pistol exploding from a similar failure. I don’t have the answer what happens, but I’d like to hear from a gunsmith who does.

    • Proud_to_be_American

      The pic showing the recovered last round case, clearly shows the primer was struck.

  • Searcher5

    The lower didn’t fail, a round blew up before it chambered. Not the lower’s fault is it? Polymer or made out of tungsten, the round blew up out of battery, or chamber if you will. The bold head blew apart, think any lower is going to handle that very well? Not likely.

  • Mr.Roboto

    What concerns me more is what caused it. Would rather know the cause than vilify a group of products when it isn’t known if the product was at fault.

  • Wolfgang

    An aluminum lower would have at least been destroyed to the point repair involves someone with a welder, we don’t use aluminum for rifle barrels for a reason. A poly lower blow out can actually reduce the pressures experienced by the shooter since the material fails a little sooner than aluminum meaning less chance of pressure build up, think of a blow off disc on air tanks.

  • PavePusher

    Bush’s fault….

  • Kenn Bishop

    The Article is very misleading it implies the POLYMER LOWER is at fault, when the pics CLEARLY show the problem originated in the UPPER! I mean look at the P-Mag I do not see any screaming about the need to go back to using steel or Aluminum Mags!

  • djsqueeze

    This is why I will never buy a polymer lower or upper for an AR- 15. I hear it happens witH bullet and forged, but they withstand fat more pressure.

  • Mike Halprin

    Based of what is a severly cratered primer and the case blow-out at the extractor, this was definitely an over pressured load. As an experienced handloader, it would be near impossible to overcharge a case with rifle powder to cause this amount of pressure. Had it just been the case “blow out”, I would say it was a weak case. Note: have experienced 1st hand a case “blow out” on a Glock 40 cal. But still the evidence points to extreme pressure to cause this crater and subsequent ejector “swipe”. From the photos, there does not appear to be any barrel bulge indicating a blockage. More investigation would be required to find root cause. IMHO.

  • georgesteele

    Yep, ah was a-workin’ up a load usin’ lasers, cemtek, and plutonyum, tryin’ ter get muzl v’losity up ter 33,000 so’s I could shoot down space stations, when danged if thuh whole thang dun ‘sploded on me . . .

    Look at the primer – the crater looks like a meteor strike; the primer hole is the size of a drainpipe, and the side of the receiver is blown off. Nope – no causative factors from polymer parts there. What is illuminating is that it looks like the lower yield strength of the polymer would have vented the pressure a bit faster than a stronger material, keeping the explosive force delivered to the expelled fragments lower. That might well be a good thing. Looks like he needs a bit more than a new polymer lower. And it might just be interesting to know forensically what triggered the explosion in the first place – hmmm?

  • Roland Kent Schmidt

    I must say, that is a novel way to create a “cut away” lower to illustrate the parts and how they fit together…

  • Ned Weatherby

    “Polymer AR Lower Exploded” wreaking havoc with the upper and BCG. Fixed.

  • Dave

    Especially the reflective belt!

    • Dave: Been reading Bohica Blues?

  • David169

    I don’t believe the lower exploded. Something caused the upper to explode which caused the lower to rip to shreds.
    All rifle centerfire cases have three zones of hardness. The neck and the shoulder are the softest to allow for good gas sealing. The neck and the shoulder are the primary “gasket”. The central body of the case expands to grip the chamber walls and reduce a little of the thrust on the bolt. The bases is the hardest and only should expand less than .001 only on the first time it is used at the maximum pressure for that cartridge. The remains of the case stuck in the bolt face clearly shows signs of being fractured. Either the case was manufactured very incorrectly and was very hard, had internal flaws in it to begin with or for some reason the powder charge detonated.
    I spent 28 years with explosives and have reloaded for 61 years now. I was licensed for steel structure demolition among other applications when I was in the business. During that time I was able to conduct experiments and always checked the planned charges on the material of structure to be brought down. Steel varies a great deal in its resistance to explosives. Copper based alloys are almost like trying to blow up a heavy equipment tire and if the blast is successful the point of material failure shows more flowing and melting than fracturing. The remains of the case on the bolt face clearly shows fracturing. This old man’s opinion is that the case had an a fracture in it that couldn’t be seen from or wasn’t present on the outside. Examination under a microscope would either confirm or deny this assumption.

  • vpats

    I gotta agree the issue here isn’t the lower assembly, judging by the damage to the upper/BCG, buffer and God knows what the chamber looks like. The upper is split, and I noticed the trigger portion of the fire control looks undamaged … unlike the hammer which is probably no more. Whatever the cause .. it was caused in the upper .. where the action is.
    I have two polymer lowers and a Windham with the poly upper and lower, all have worked as they should and I haven’t seen a hint of trouble. No doubt this story will lead to “… did you hear that ALL polymer lowers blow up, I wouldn’t have one ….”, as this guy is reaching for his Glock. I was in a large Sporting Goods retailer (you all know the name) I was in the gun section of the store at the same time as a salesman was pushing an AR-15 of normal construction .. and he advised that the customer would be better off staying away from these new fangled polymer AR’s … because “.. I’ve seen them BLOW UP ..” keeping decorum in mind I kept my mouth shut … and left.

  • pepelapiu2004 .

    Holly cow! Never seen so much debate about merely the tittle of am article. Inhale, relax, take a sip.

    • robocop33

      Careful there pepe, you said “Holly” instead of “Holy” so look for these same people to take you to task and ask you or more likely demand that you explain that by asking you if you were saying that the cow only ate Holly from Holly Bushes or something like that.

  • Wow!

    Obviously the failure point is not the polymer lower. Nothing in any lower will cause the bolt to fracture. This either was a failure from the upper, or more likely, ammunition.

  • Glenn Schantz

    What causd the failure? Was it a double feed and ignition or what, the article makes it look like polymer lowers are unsafe and I know there are some very good ones out there like the omnoi hybrid so a follow up with the cause, the make of this lower and as much info as possible would be much appeciated, especially as I am in the middle of a build using a polymer lower, lol.

    • Doom

      looks like case failure, which would kill most guns. just really killed the polymer in a spectacular way instead of banana peeling a side or two off of an aluminium lower or upper as the gas looked for a place to escape.

  • Billy Jack

    On the 12th day of Christmas my true love gave to me…

  • drew

    Was shooter using handloads? A double charge of powder perhaps?

  • L. Roger Rich

    This is what is called FAKE NEWS. nicholas

  • tenmillimeter

    My money is on bad ammo, either a double powder charge, or the bullet not crimped or maybe out of spec…or the neck not prepped correctly… allowing the bullet to be pushed back into the casing on being chambered, then detonation causing a pressure spike. Gloves and eye pro FTW!

  • ErSwnn

    I see nothing stating a cause to the problem. Given the debate over materials wouldn’t the cause be germain to the discussion? I’m thinking a handload gone wrong. Would the same issue have caused the same damage in an aluminum lower?

    Being old school, I still want metal. But one thing I’m wondering about, how often does such a malfunction happen with factory rounds? I’ve had only one such incident and that was with an old Titan Tiger, a very cheaply built gun. A revolver, the backstrap separated. In such a gun I expect such poor quality but an AR? So, what is the range report of ARs coming apart? I’ve never seen it happen. But I have seen the results of poorly made handloads in other guns.

  • whamprod

    So…. I’m not clear on something….. Nicholas, are you implying that the polymer lower was the cause of the failure, or are you simply saying that it failed more spectacularly when the gun kaboomed than it would have with a forged or billet lower?

  • jonp

    I’m going out on a limb and say a casehead failure of the round.

  • Skyviking

    Not the fault of the lower. Who made/assembled the upper? SAAMI .223 Rem., NATO, or Wylde chamber? MIL-Spec parts (I’d wager Not)? Bolt headspaced?

  • George Flynn

    Jeez Guys why all the Fuss over the Headline ? Just make sure you Clean your Weapons and wear Eye Protection , Gloves wouldn’t hurt

  • robocop33

    Everyone seems to be upset at the use of the word exploded! Why don’t you write to the manufacturers of just about all products who show you an ‘exploded’ view! Go whine at them that the part or product didn’t really explode. Better yet just get a life already! The lower DID in fact ‘explode’ (as in come apart in an explosive manner) and it was because the ammunition caused an EXPLOSION in the upper portion of the firearm.

  • JamesDrouin

    Lots of mis-information represented in the images … for a “fact” the cartridge sits in the “chamber” when fired. Thus, the lugs on the locking bolt and/or chamber “failed”, either because they didn’t fully engage, or were structurally deficient, or the cartridge was charged with an incorrect load, or, or, or.


    Looks like it fire out of battery to me. It would be nice to know the ammo manufacturer, and know if it was a reman load. Also would be nice to know if it was a malfunction (like firing out of battery), if this was one of those torture tests, or if this was just out of nowhere while plinking.

  • Bob

    I would like to know the cause of the KB and if it was related to the polymer lower.

  • jonp

    That primer looks pierced. Looks like it might be an overload, possibly a double charge.

  • Tp

    well what brand, caliber, was it fed the wrong ammo?? .22 brass on the bench, looks like a small .17 center fire brass stuck in the bolt, someone put a high pressure .17 in a gun that was not made for it, just pictures, no article?

  • BrotherLazarus

    From what I gathered first as a shooter and continued seeing through getting into gunsmithing proper, a pretty large portion of the shooting community believes in the myth of the Accurate Gun making up for shortcomings in their own marksmanship.

    A lot of people are simply minute of badguy, and there’s nothing wrong with that as long as they accept their limitations in either training or physical abilities and don’t place the blame on the platform. Since I trashed my back I just can’t lug and fire a .300WM with pinpoint accuracy–it’s not the fault of the cartridge or platform, I just don’t have the upper body strength and steadiness to throw sub-MOA groups out at long range anymore.

  • Frederick Palmer

    Am not a user of polymer lowers but am not a “hater” towards them either…and from what happend to the BCG (!) it’s clear that happened here would have also destroyed any aluminium lower.

  • Ed Byrd

    When the lower is aloy , the upper explodes. The explosion will always go through the weakest link. I’d rather lose a finger to a polymer lower, than both eyes to an alloy upper. Google search ” ar15 kaboom “.

  • John

    It had nothing to do with the lower. When I saw the title, I thought the buffer tube tower broke off or something. Catastrophic failures suck, and are the reason why you should always wear eyepro on the range.

  • Larry Lawless

    Would you shot a pistol with a Polymer upper? Of course not unless you were to shoot a single shot .22 maybe. But a 9 mm or .45 , no way, so why a polymer lower, nutz.

  • Larry Lawless

    I have a 155 year old rifle I would never feel afraid to fire, it was built well then and fires excellent today, the barrel and firing chamber is metal, not polymer.

  • Franco Eldorado

    It looks like it could have been caused by an out of battery detonation or maybe a squib load. I doubt it was lower related. I have a polymer lower that I dedicate to a 22lr Conversion but it does fine as a 5.56 too. I do prefer forged lowers however.