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. Thanks Scot – I’m glad the project has been of interest to other enthusiasts! While I found that this is not in fact the first 3D printed firearm to be tested (though what exactly _was_ first is still a bit sketchy – see my latest post), it’s still a very new capability for the field. I’m eager to see what other hobbyists come up with!

  2. Hey man, Great work. It’s people like you who push the medium they are working.

    Since I am not an expert on guns, do you know f it’s possible to print complete guns using this technique? Would be crazy if one could actually do that. I am a 3d artist by trade so that’s why it’s fascinating.

    Also your printer is factory type expensive ones, no? I thought you were using the typical $2k 3d printers we have now, before reading your article.

    Anyway ignore the haters, amazing work.

  3. Yes, it should be possible to print something that can be defined as a gun by nothing more than 3D printing (and a few rubber bands), which is precisely what the Defense Distributed project hopes to achieve. However, such a device would be little more than a plastic ‘zip gun’, and would be just as likely to injure the shooter as the target. Like wooden cannons, such devices would be of minimal utility, but would still function.

    Yes, my machine is one of the big professional ones, but it’s quite old and didn’t cost me much. Regardless, printing the AR lower can certainly be done with a Makerbot or other $2k printer.

  4. Would it have been better to print with layers running along the long axis?
    Surely most of the forces involved are axial (w.r.t the barrel)?

  5. Well, the AR-15 receiver is a complex enough part that there probably isn’t one best orientation to print it in. I opted to build mine with the Z axis running along the magwell broach axis to ensure that the magwell would be sized correctly, and to minimize my use of support material (and having to clear out the support material from various areas). Plus, it provided the best aesthetics since very little of the exterior surface was supported by breakaway supports.

    In reality, I think orienting the model to achieve dimensional accuracy (especially the buffer threads) is more important than trying to orient to account for imparted stresses. At least at this stage in 3D printing technology.

  6. Hard to say without knowing exactly what resin they’re using. However, they list the tensile strength at only 1000psi, which is downright feeble. ABS plastics used in printing such as the PA-747 in Makerbots and the AG700 used by Stratasys are well over 5000psi in tensile strength.

  7. Have any of you actually watched or used a 3D printer. I haven’t, but I imagine it is an amazingly complicated and slow process. Just because it is called a “Printer” does not mean you can just go down to Best Buy and pick one up for $80, load it with ABS, print a file to it, and have a lower you’re ready to go on a killing spree with.

    In most cases you have to build the printer yourself, OR buy one for a hell of a lot of money. Thousands I imagine. And then, its hardly the best way to make lowers… you’re building up a piece a tiny thin layer at a time, and its slow, and not a particularly strong piece. Imaging building a lower with a can of spray paint… lay down the mask… spray paint… wait to dry, repeat… repeat… repeat… until you have an inch thick piece. Yeah. Not very strong, not very fast, not very economical.

    And just because something is illegal, does not mean you shouldn’t do it. People jay walk all the time; that is illegal. People speed on the highway all the time; that is illegal. People trespass all the time; that is illegal. My bet is you’ve done all three. Grow a pair.

  8. That’s always been my issue with the movie “Alien” (the first one. The James Cameron sequel is excellent). The entire basis for this movie is that they are trapped, weaponless, on their ship with the Alien.

    The basic fact is that tool==weapon. A hammer is a fantastic club. A screwdriver can stab someone remarkably well. Any advanced spacefaring culture is going to have remarkably impressive tools, and those tools can be made to also perform as weapons.

    Larry Niven pointed this out in his first contact story about humans and the Kzinti, The Warriors

    So the notion that you can create a weaponless society is retarded and clueless. Your best possible bet — if you’re determined to try it, *I* certainly would advise against it for much the same reason suggested in The Warriors, is that suggested in The Warriors and many other stories in Niven’s Tales Of Known Space future history. You’d have to “reprogram” violent behavior out of the society, genetically and chemically.

  9. Grospoliner also misses the fact that there are Computer Controlled Milling Machines and Lathes. I figured this would be the first source of computer modeled gunwork, and perhaps (given that you’re using a more advanced production unit) that will still be the case — but they can’t control guns any more, either way. If they attempt to ban them, then they will find a cottage industry in them springing up, and all the laws they can pass will be as worthless as Marijuana laws in controlling the actual flow of them.

  10. Actually, according to the 1963 gun control act YOU are allowed to make your own gun, unregistered, and keep it, as long as YOU make the receiver, and only YOU use it.

  11. You’re correct right up to “…and only YOU use it”. I can still let others use it at the range, and can even let them borrow it for the weekend (if I mark it with my name, city, and a serial number). I can even sell it to someone if I decide I no longer want to keep it (but as I noted, it is illegal to make with the intent to sell/transfer, as then I would need to be a licensed manufacturer (type 7 FFL)).

  12. Can you make a pistol magazine with your equipment? Taurus international has a habit of discontinuing pistols and spare magazines for some of the ones still made. I have a 709 slimline and need a couple of mags for it. There are none to be found. I think they sold a lot of pistols and there would be a good market for some. Please advise.

  13. Yes, magazines have been printed – Defense Distributed ( developed a printable AR-15 and AK-47 magazine. Pistol magazines are potentially a little trickier, as the allowable wall thickness is a little more limited. I suggest posting in the DEFCAD forums ( and see if somebody might be interested in designing one. I think replacement magazines are going to be a very popular firearm application of 3D printing – I have a single magazine for the PSL rifle I’m building, and they’re getting quite expensive if you can even find them.

  14. I’m new at the 3-d printing. Where do you find the program for it the ar-15’s. I would like to do the .22’s. Sounds like fun. .223-sounds like a bug out gun. I have the xyz davinci 1.0. I was informed that it was capable of printing said unit. Pla filiment. Then again. I’m probably totally off course. Thank you. Shake..

  15. This is amazing! Out of curiosity, have you experimented with 3-d printing front sights (for the AR-15)? Specifically 1/8 MOA front sights?

  16. No, I haven’t tried any sights – FDM printing would be really coarse for such an object, and I’d much rather have a proper metal post for that application. If you’re shooting for (pun not intended) 1/8 MOA, you’re really far into magnified optics territory anyhow (I seem to recall that the stock sight post winds up having an effective width of 12 MOA).

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