3D Printer AR Rifle Fail

The Defense Distributed project tested a AR-15 lower they printed with a upper receiver chambered for 5.7x28mm FN. The 5.7mm cartridge generates a lot less recoil than a full power 5.56mm / .223 round.

Surprisingly the buffer tube threading held up, but the off axis force of the buffer tube against the ring caused it to fail. There is a write up about the incident at the Wiki Weapon blog.

[ Many thanks to everyone who sent in this tip. ]

[Hat Tip: Boing Boing]





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.


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  • Schlumper

    Doesn’t the fact that this upper is recoil operated using one of the heaviest buffers on the market put more stress on this part of the receiver than .223 would?

    • John

      If it was me I would start with a .22LR upper and then slowly work up to bigger calibers. Safety first.

    • BF

      I would imagine there is more force with the 5.7 than a 556. I have a 9mm upper and I know the blowback recoil is much more violent than my standard midlength 556 upper.

      • Icchan

        Could be length of travel issues? The 5.7 is smaller, but much shorter in OAL so I imagine the buffer could be reaching the end of the stroke early and hammering inside. That could be one cause…

        …though honestly I think the main reason is the weak plastic. Like Alex said, make mold masters this way and THEN make your guns.

      • G

        5.56, in 5.56×45, refers to the diameter of the barrel’s rifling(*). Both 5.7×28 and 5.56×45 use .224″/5.7mm bullets.

        (*) 7,62, in 7.62×51, also refers barrel’s rifling. 7.62mm is .300″. 7.62×51 and 300 Winchester Magnum use .308″/7.82mm bullets.

  • Anthony H.

    Hey, that’s not terrible. Just need to insert some reinforcement into that thinner area between the buffer tube and grip. Maybe force two metal rods down it and it could keep it from snapping. Not bad for a first “real” attempt. At least it didn’t have a catastrophic failure.

  • Reverend Clint

    this might be good for the bolt action uppers since nothing violently moves in the buffer tube.

    Cool to see them do a non buffer tube version like the para usa/LR 300

  • Alex Nicolin

    Instead of trying to use the printed plastic components directly, they should try to make them into cast molds, and pour some melted aluminum into them. Even investment casting should work, as aluminum melts at about 1250F, while most plastics melt at much lower temperatures (550-700F) so it will be quickly displaced from the sand mold. Aluminum itself is easy to melt, and could be done at home, with inexpensive equipment.

    What most people that think of “plastic” guns don’t realize is that the plastics used for gun frames are not printed, but mold injected, and are many times stronger than what they could achieve using the first method. It’s all about the polymerization process and the fillers (carbon or glass fiber). For example, one of the most used plastics is Nylon 6-6 CF 20%-30% (Glock frames are made of it), which has a tensile strength of 32-38,000 PSI. Almost as strong as 7075 aluminum, used to manufacture AR15 upper/lower receiver.

    Another problem would be the heat. AR15, being direct injection, venting hot gas in a plastic receiver, would “cook it up” in no time.

    • El Duderino

      My knowledge of metallurgy is not great, but wouldn’t you just be making pure aluminum with that technique? Pure aluminum is not very tough.

      • Alex Nicolin

        Depends on what you are melting and pouring into the mold – pure aluminum or an alloy. You can get a billet of alloy aluminum, melt it down, and pour it into the mold. Of course, this wouldn’t work with sintered composites, as the that technology is reserved for metals which won’t usually mix. But for usual alloys, it should work (7075 is castable). After you get the piece out of the mold, all you need to do is deburr it the quench and temper it to the right toughness. Lots of people already make car parts this way, so why not gun parts?

    • denny

      This is MIM (metal injection molding) process, is it not? There might have been some new developments since I worked with it. We used steel powder as the core material (with polymer fill which was melted away prior to sintering).

      • Alex Nicolin

        No, MIM is a whole other technology, and it is impossible to do at home, due to complex technological process and high volume of feedstock needed. I was talking about basic investment casting, also called “lost wax” process (well, lost plastic in this case).

    • Avery

      I was about to reply to Lance’s comment exactly about this.

      It’s pretty much the closest to 3D printing metal right now, although you’re adding a lot more steps to the process.

  • I still think this is awesome. The technology that is going into these 3D printers is amazing. We’re a ways off from being 100% on the AR lowers, but we already have some 3D printers that can print using metal, so it won’t be long before we can print off a full blown AR lower that’s just as good as the forged lowers we have now.

    The possibilities with this technology are nearly endless, and we’re just exploring the tip of the iceberg at this point.

    • Forrest

      Hope you’re right, but for instance I don’t see how 3D printers could produce high-quality machined barrels, or any metal part that could fit the necessary quality for a rifle.

      • Alex Nicolin

        For barrels, the inverse process would be much more efficient. Instead of adding material using laser local melting. You could use it for drilling the bore and etching the rifling inside it with great precision.

    • Forrest

      To Alex Nicolin :
      Yes, but you’re talking about laser cutting, which is not common technology. As a previous commentary (Marc) said, these are very expensive machines. The background of this topic seems to be affordable ways for mass-produced rifles.

  • John Doe

    Well things can only get better from here. Can’t wait to print my own minimalist handguard one day, with only what I need. Or a grip that feels perfect in my hand. Or a stock that has the perfect cheek weld.

  • denny

    That’s nuts! The user must have good med insurance I presume. The material used in SLS (select laser sintering) does not have any real world strength to it. Models such made are used merely for visual presentation.

  • Lance

    If only they can 3d print aluminum.

    • Marc

      They can, it’s called direct metal laser sintering. The machines are just a lot more expensive.

  • Adam

    I don’t think he’s nuts. Does anyone know of a catastrophic lower failure that resulted in injury? I have seen lowers that have failed but they are all tied to events that began in the chamber (or worse should have began in the chamber but did not). The worse thing I can think of should be the buffer tube separating from the lower like this one did and sine it is braced by the users shoulder it is a non-issue.

  • Nathaniel

    The problem isn’t that it’s made of plastic, it’s that printed plastics are terribly weak.

  • JAFO

    I’d like to see them try this with a piston upper- I don’t think they’ll have the same failure, as the spring and buffer won’t be beating the rear of the printing.

    • Huh?

      You mean like an LR300/Para TTR upper, that doesn’t require a buffer, buffer spring, or buffer tube, and isn’t actually what we’d commonly call a piston upper at all?

      Most AR-15 gas piston uppers still use buffer, buffer spring, and buffer tube, and almost a standard bolt carrier. I think you’d still have the same problem, and “mortaring” to remove a round stuck in the chamber would still put a lot of stress on a plastic/polymer lower anyway.

  • gunslinger

    would have thought a .22 would have been a good start.

    but i was looking at doing an Omni 5.7 build. not so sure now.

  • Ian

    How completely unsurprising! A 22lr would work, for a while. Printed plastic has very very little tensile strength.

    Printed metals are a bit stronger, but still quite weak. Afaik you can’t print Aluminum yet.

    Face is, 3d printing is for prototyping currently and will be for the foreseeable future.

    • anon

      ARCAM of Sweden can already print in Titanium and Cobalt Chrome alloy, and they claim strength better than cast.

      I’m not particularly up to date on this, but I’d assume you can get strength equivalent to sintered powder parts.

      Additive Manufacturing is still in it’s infancy in a lot of ways, but it is no-doubt getting better all the time.

  • Hami

    Looks like a success to me. Step one is print a lower that shoots. Next is to make it reliable and repeatable. Rome wasn’t built in a day.

  • Spencedaddy

    I wonder what plastic they are using? they just came out with some printheads that can handle PEEK plastic…which is more or less aluminium!

    • Ian

      The weakness isn’t the material, it’s the process. They have been printing nylon for years now but it’s still completely unusable compared to an injection molded part.

  • tib

    The real problem is the method of 3D printing. These printers lay down a thin bead of material to fill in each layer and build up the part one layer at a time. This has two fundamental problems for working parts.

    1) The tensile strength in the direction perpendicular to the layers is horrible, regardless of material used. The failure mode is almost like delamination and can’t be avoided without some serious post prototyping work to fuse everything.

    2) Being made of essentially a string or line of material leaves not insignificant gaps in the final product, especially near the exterior shell. As soon as you put a shear stress or torsion near these points, a crack will develop and then there is very little to stop it from propagating all the way through the part.

    I’ve done alot of stuff with rapid prototyping and it works fine for seeing how a part feels or will interface with something else. However, for any high stress applications, there are much better ways to quickly make the parts.

  • This is pretty much what I expected using larger than a 22LR in a printed upper. But having done it myself, making molds and casting in aluminum isn’t horribly difficult in the back yard. Use the printer to make the prototype, mold it, and pour cast a copy in aluminum. You could even add reinforcement to the rear since that’s the most likely fail point.

  • Mike Knox

    Well, here’s something they forgot about Polymer Frames for Firearms: Steel Inserts. Maybe they should have done proper research..

    • gunslinger

      yeah, except it’s a bit hard to print those steel inserts…

      • Mike Knox

        How they’re placed is in the name, d’uh..

  • Esh325

    It could very well be a successful concept some day.

  • I am curious what method of printing did he use? What material specifically. There are some rather strong and flexible materials out there for 3d printing.

    I wonder if they over engineered the area where the buffer tube attaches it could have prevented the crack.

  • Partizan1942

    Am I the only one that is more interested in seeing how they make that lower? I mean to me the manufacturing process would be more interesting to see. Maybe if I could see that I would not call this a total fail like many do. Also, if you can print a lower, why not rather print a mold for it and make a cast? Could be stronger even if one uses plastic.