Gunsmithing with a 3D printer – Part 2

I know I’m not alone in having printed an AR-15 lower and test fitting it with internals – this fellow printed an upper to go with his printed lower, and another Thingiverse user just printed an AR-10 lower! I’d be pretty hesitant to use a printed lower with something as powerful as .308 (hence why I’m starting with .22), but I am impressed that a bulked up AR-10 lower can still be printed on something the size of a Prusa Mendel.  I’m sure many others have also printed AR-15 lowers, but I can’t find any indication of anyone having actually fired one.  I’m sure my printed lower will hold up just fine, though the response of many firearms owners is essentially “You’ll shoot your eye out, kid.

Before I can put my money where my mouth is, however, I need to actually have a complete upper receiver.  This weekend I finally got around to attaching the CMMG pistol length barrel that I have to an upper that I purchased many years ago.  I’m not sure why CMMG decided to stake the front sight/gas block in place when it needs to be removed anyhow to attach a barrel nut, but I managed to drive the retaining pins out of the gas block, remove it, slip a barrel nut in place and re-attach the gas block.  Why am I going through this trouble?  Because due to the quirks of US law, a receiver can be switched back and forth between rifle and pistol configurations only if the first incarnation of the receiver assembled into a complete gun was as a pistol.  I don’t want to limit myself, so the printed lower will begin life as a pistol in order to comply.

This subject of the upper receiver brings up another point – people have asked me if the upper could be printed as well, and I’m not nearly as confident of such a part as I am of a printed lower.  When installing the barrel to the upper receiver, I found that the minimum barrel nut torque is defined as 30 ft-lbs (with a maximum of 80 ft-lbs allowed when ‘timing’ the barrel nut so that the gas tube will align in one of the notches on the barrel nut).  I really doubt that an unreinforced thermoplastic can take up to 80 ft-lbs of torque on 1.25″-18 threads, especially given all the discontinuities present in a printed part.  It’s probably sufficient to use less torque, as the barrel nut simply keeps the barrel attached to the upper receiver (and I believe the Bushmaster Carbon-15 uppers, which are a carbon reinforced polymer, specify a lower torque).  All of the force from the shot fired is held between the bolt lugs and matching faces on the barrel extension, not between the barrel nut and upper receiver.

Assuming you had printed an upper receiver and didn’t overtorque the barrel nut, it would probably work fine.  For a little while, at least.  The problem with the AR-15 and its derivatives is that the gun ‘craps where it eats’.  Many modern rifles are gas operated, meaning that they divert some of the hot expanding gases from the barrel to actually recock the gun (as opposed to being recoil or blowback operated).  The AK-47 and AR-15 are both gas operated, but the Kalashnikov has the hot gases acting on a piston very near to where the gas has exited a tiny cross-drilled hole in the barrel.  The piston is connected to the bolt carrier, and every time the gun is fired, gas pressure on the piston pushes the bolt carrier back, cycling the gun.  In the AR-15, the gas is directed through a long tube all the way from the hole in the barrel right up to a ‘gas key’ attached to the top of the bolt carrier.  This allows for much less reciprocating mass (which means that the AR-15 has much lower felt recoil than its Russian counterpart), but with the disadvantage that all of those hot gases (and other crud that comes from burning gunpowder) are blown right into the chamber above fresh rounds in the magazine – hence, ‘craps where it eats’.  Since FDM style 3D printers use thermoplastics as a feedstock, these hot gases will undoubtedly start melting a printed upper.  In fact, I’ve heard reports of reinforced polymer uppers starting to melt after repeated rapid fire.  Fortunately, piston systems are becoming more widespread on the AR-15 platform, which would eliminate the ‘hot gas melting the upper’ issue, but I’d still be hesitant to try using a 3D printed upper even for just rimfire cartridges – reinforcement would be needed, I think.

Since I’m using a CMMG .22 kit, it doesn’t need a buffer and buffer spring (which is great, as I don’t have those parts anyhow).  In fact, it doesn’t need anything attached to the rear of the lower receiver at all, but I wanted to have something in place to help provide support for the ‘buffer tower’ (the ‘loop’ at the top rear of the lower receiver). More importantly, I wanted an excuse to finally use the nice 1-2″ thread pitch micrometer that I bought several years ago.

I stuck a piece of 1.25″ scrap aluminum rod in the lathe, and turned some threads onto it.

When the micrometer indicated I was getting close, I threaded on an actual aluminum lower to test for fit.  Afterwards, I opted to fit out the lower with internals as well, as I figured it was prudent to test the untested upper and .22 conversion with a ‘proper’ aluminum lower first.

This morning I hunted around for ammunition, which took me a good 20 minutes (while I am a firearms enthusiast, I don’t think I’ve fired more than a dozen rounds or so in the past 5 years).  After realizing that I had no .22 ammo (yet discovered cartridges for guns that I do not own), I made a stop at the manliest store on the planet to pick some up (if Bruce Campbell were a store, he’d be Fleet Farm).  I then headed to a top secret testing facility (Dad’s farmland) and carefully assembled the upper onto the aluminum lower.  Absolutely nothing had been previously tested, and this was actually the very first AR-15 I’ve assembled (or even owned), so it was with a fair bit of trepidation that I loaded a magazine into the gun (with only a single round – always test unproven systems with a single round to begin with).  After cocking it and carefully letting the bolt forward to chamber the round, everything looked to be in place, so I aimed (as well as one can ‘aim’ with nothing attached to a flattop upper) 20 feet away into the dirt and fired.  Everything worked fine, so I reloaded with 2 rounds and repeated, followed by 3 rounds.  All systems functional!

I switched out the lower for my printed version and double checked the operation.  Would it hold up?  Again, one round in the magazine, cock the gun, squeeze the trigger, and…  Wouldn’t you know it, I shot my eye out.  Just kidding – it functioned perfectly.  Testing again with 2 rounds, then 3 rounds, then a full magazine.  Everything ran just as it should, magazine after magazine.  To be honest, it was acting more reliably than a number of other .22 pistols I’ve shot.  I ran close to 100 rounds through the gun before getting annoyed with not actually being able to aim at anything, and decided to call the experiment an overwhelming success.

To the best of my knowledge, this is the first 3D printed firearm (as per the definition in the GCA) in the world to actually be tested.  However, I have a very hard time believing that it actually is.  My Stratasys is a good 15 years old, and Duke Snider’s original AR-15 CAD files have been floating around on the ‘net since early 2000.  As such, I can’t imagine that I’m the first person stupid adventurous enough to actually pull the trigger on a 3D printed receiver.  If someone has beaten me to it, please leave a comment!

80 thoughts on “Gunsmithing with a 3D printer – Part 2

  1. You have just turned the 3d printer into ‘dangerous goods’, thanks a lot. There is always one that has to wreck it for the rest of us. Now the government will try to take them away or legislate them.

  2. Just like the government took away and legislated all the mills and lathes that home gunsmiths had been using for decades. Oh wait, that never happened. Being able to make a firearm at home is nothing new – in fact, folding a receiver for an AK-47 is a very simple project that requires nothing more than hand tools. The process of 3D printing a receiver is simply using a different type of machine than in the past, nothing more.

    Just as with a firearm, the responsibility for the machine’s usage lies with the operator, not the device itself.

  3. That is awesome. I am not a gun guy myself, but I enjoy the craftsmanship and the whole mechanical aspect of it. And I honestly thing- this is considered progress as far as 3d printing is concerned.

    To the anonymous poster. Lathes, and routers (CNC or not) are used daily (and for manymany years) to create gun parts- they are not and never will be- considered dangerous goods. Hammers create swords, wooden branches create arrows…Please think things through…

  4. Thanks! As mentioned, I’m really not much of a shooter myself, but firearms are the intersection of so many fields of interest – metallurgy, materials technology, heat treatment, surface treatments, etc. that I find them fascinating pieces of engineering. Building one always gives me new appreciation for the intricacies of the design.

    And I agree – showing that a functional receiver can be 3D printed illustrates just how capable the technology is. Hopefully we’ll see 3D printing evolve as a suitable small scale production method (which is exactly what Stratasys is trying to promote with their Fortus machines).

  5. Did you have to register your home-made lower? If so, how did you go about doing so?

  6. Zero registration required in Wisconsin, just as if I had machined an 80% lower to completion – laws in your state may differ. Check marking requirements as well – in WI, no marking is needed on a homemade firearm, but I would have to mark it if I were ever to sell/transfer it to someone (but as with all homemade firearms, making it with the intent to sell/transfer is illegal).

    The only registration that would be required on a federal level is if I wanted to make it into an SBR, but as that takes $200, a good 6 month wait, and approval of a Chief Law Enforcement Officer, I have no plans to do so with a printed lower!

  7. If you’re willing to go down to a .22 short, and expect only one shot, I very strongly suspect you could print a neat little pistol. There are, of course, a lot of practical and legal issues with this…

  8. Hi Vik! Was curious to know if you were interested in this little experiment…

    Yes, I’m sure you could print a small ‘Liberator’ style .22 short pistol, though you’d certainly need a proper steel barrel and firing pin (possibly a spring as well, though rubber bands may do the trick). I may have to ponder that a bit more once I bring the AR-15 experiment to some sort of conclusion (fired the lower with actual .223 today and will probably do a short post on it).

  9. I’m sure this is on your web site somewhere, but I don’t want to tax it with a search any more than it already is, but can you tell me what sort of 3D printer you used and what material the receiver was made from?

  10. I see from the previous post that you’re using ABS, but I’d still like to know which Stratasys machine you’re using.

  11. My printer is a Stratasys FDM 1600 – it’s a mid-to-late 90s machine. As for material, I used Bolson ABS – it’s roughly equivalent to Stratasys P400 ABS, which is some sort of injection molding grade ABS as best I can tell (wish I could find out exactly what resin they’re using).

  12. You wouldn’t happen to do commission work would you? There’s a replica of a gun from a anime I watch that I’d very much like to have a static replica of if possible.

  13. Let me guess – Togusa’s Mateba or Vash the Stampede’s revolver? I have done commission work from time to time – I’ll drop you an email.

  14. Excellent work. Reports from the “firearm illiterate” press on your accomplishment are entertaining. They obviously should read your blog. Worse case they may need a press release at about a 5th grade level to explain that you didn’t actually produce a 100% printed plastic gun. I’m looking for the poor fool who undoubtedly has already written about your 100% printed plastic ammo.

  15. I actually did attempt to take video during the initial test, but naturally I messed it up and didn’t get anything. Once I resolve the issues with the .223 upper, I’ll try to get a little video of the operation.

  16. Hadn’t even considered this application of 3D printing. Unfortunately, this will become a issue now that you’ve opened the door. While mills and lathes are used in production of fire arms, there is a difference in ease of use between them and 3D Printers.

    It takes a skilled machinist to use lathes and mills and with the cost of 3D Printers coming down to comparative levels (while still being somewhat prohibitory cost wise for both machines), the arguments will focus on the ease of use of 3D printers and access to ready made designs.

    You also know fully well that the law doesn’t keep pace with technology development (else we wouldn’t have the issues of piracy and internet regulation cropping up every few months, or any number of stupid situation involving the police and recording devices). So before you get indignant about someone pointing out the inevitable conflict which will arise due to your actions, you need to sit down and actually realize that yes, your actions will result in some future legislature regarding firearm production and 3D printers.

    Obviously if you didn’t do it someone else would have so you’re hardly to blame for whatever does come around.

  17. Congrats, your small endeavor is on first page of biggest Polish web site and as expected with text “first 100% printed plastic gun” 🙂

  18. Hey,

    Am a reporter and think this is really interesting – would be keen to have a chat about it at a bit more length if you’d be willing. Would you drop me an email if so? Thanks!

  19. I’d like to point out that using a drill press is even easier than a 3D printer, and far more of them are ‘in the wild’. In fact, thousands of people have used nothing more than a drill press to complete an 80% lower receiver (according to Nathan @ Tactical Machining). As far as requiring a skilled machinist to operate a mill or lathe, well, I am exhibit #1 in refutation of that claim. Many years ago, with zero training on the lathe at work other than “move these handwheels to make the tool bit move that way”, I was able to machine a new bolt for my paintball gun. While machining a lower receiver on a mill is certainly a more complex project, the abilities of a true machinist are not required (though I admit it’s a romantic notion).

    I respect your point of view and agree that law does not necessarily keep pace with technology (you cite excellent examples), but I disagree that the spread of 3D printers will force some sort of legislation, and I maintain my position that 3D printers (as applied to firearms, at any rate) will be viewed as simply another machine type.

  20. Pretty awesome, bro! I wish I had a 3d printer…all those expensive AR-15 “furniture” wouldn’t cost as much after a few add-ons and removals (no use re-inventing the wheel..).

    One thing did concern me while reading this post. On this page, the second paragraph’s fifth sentence reads, “Because due to the quirks of US law, a receiver can be switched back and forth between rifle and pistol configurations [i]only if[/i] the first incarnation of the receiver assembled into a complete gun was as a pistol.” I really don’t want you inadvertently breaking federal laws, and this isn’t true. It’s been the ATF’s view that as soon as you attach a buttstock to any pistol, you have created a rifle. This new rifle cannot be converted back to a pistol without having it registered as a Short Barreled Rifle.

    Congratulations on your success! I’ll be happy to email you supporting information at my leisure (busy with the job search and school…gotta make the money for guns and ammo! haha) if you’d like to email me.

  21. You’re nearly correct, but not quite – I suggest having a look at the ATF’s ruling based on the 1992 Thompson/Center Supreme Court case. If you were to attach a buttstock to a receiver that also has a pistol length barrel attached, then yes, you would have just illegally created an SBR (assuming that you had not gotten a tax stamp for creation of the SBR). However, if you make sure to fully remove the pistol barrel (by removing the upper in this case) before attaching the buttstock, you are in the clear. I have two uppers I use – the pistol upper, and the rifle upper. I make darned sure that the buttstock is not attached to the lower if I intend to put the pistol upper on it! As mentioned in the post, I can only switch my lowers back and forth because they began life as pistols – had they first been assembled as rifles, then you’d be correct about illegally making an SBR, regardless of whether or not they had a buttstock attached.

  22. Have a 3D printer, create weapons and rock the cinema. Great thing for the mentally sick. Happy news for those criminals and retards who are not allowed to purchase weapons.

  23. [sarcasm] Truly, this is a shocking development. Before the advent of 3D printing, it was entirely impossible for criminals to get weapons. [/sarcasm]

  24. I just updated my Facebook status with “Yes, ‘Man Who Prints Assault Rifle At Home’ is my brother. *facepalm* ” (Yes, yes, I know it’s a “semiautomatic weapon”, but that’s what the media is calling it.)

  25. Instead of correcting people you could just realize the implications on society that you are creating. Doesn’t matter whether it’s a rifle or a pistol, you are showing criminals how to get weapons even easier than before. I hope you can handle the backlash after the first mass killing with a printed gun using your “easy” plans. My favorite part was how a lathe (a craftsmans tool) is easier to use than a printer. Haha have you ever heard of innovation? With the right plans… Just press print. I know, I know it wasn’t your gun that did the killing.

  26. I correct people because the entire purpose of this blog is to share technical information, not to discuss politics – there are plenty of other outlets for such debate.

  27. I wish I could “just hit print” and my home 3d printer would just start printing this cookie cutter my wife wanted me to print… But I can seem to get the settings right to keep the part from curling and lifting off the bed, plus I cant get the little globs to stop building up on the part because the temp isnt just right. then the stepper motor keeps sticking bc of the bur that is on the drive screw… oh and thats not to mention that the over hangs on the design and trying to calibrate the second printer head (which the majority of printers still dont have) and get it to print support material…. I have had this for 4 months now and am still struggling with it. Fix one thing and another problem comes up not to mention the changes in temperature outside that play a large role in how the printer printers that day….

    I ve never had training or anyone to show me how to use a mill or lathe but I walked up to one last summer to complete my College Thesis project (a futuristic Compound Bow design) and had no trouble creating all the parts for that on both the mill and lathe at my school. Looked like a production product when I was done. I had a lot more to show for my 4 months of work on the mill and lathe then I do so far with my cheap 3d printer.

    Might I suggest that it was your 3d printer that did the killing after you threw it out your window in frustration as it landed on someone walking by…..

    And even though printers are cheap, what kind of criminal is going to want to spend more money then a gun would cost him to buy a printer, take the time to figure out how to use the printer (possibly buy a computer) search and download the files, order printer material, order all the other parts that he needs (since we are not talking about printing a WHOLE gun here, just ONE part) assemble the firearm (have the knowledge and skill level to assemble it and do it correctly), buy ammo, test fire, then take off to commit his crime. Hell, by that time he might forget what he was going to do with the gun…..

    He could easily acquire a firearm a whole lot easier for still a lot less money and a shorter amount of time….

  28. I’m a bit late on this discussion, but congrats on your success! It’s a rare thing that one gets to be the first to do something that no one else has done before.

    Thanks for inspiring many of us that are tech geeks and firearms enthusiasts, too! I’ll be building a 3d printer before 2013 is over.

    Keep up the good work and although I don’t have to tell you this, don’t listen to the folks that are terrified of firearms. They’re not worth your time.


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