Gunsmithing with a 3D printer – Part 1

I’ve used my Stratasys to prototype out various ideas for paintball gun parts, but the concept of using it for actual firearm parts hadn’t really occurred to me until early last year.  I first thought of making some dummy 12 gauge shells to test out the action on a Remington 870, and then thought of using it to test out 1911 pistol grip panel ideas.  Gun manufacturers have been using rapid prototyping for years, and the concept is now making its way to the hobbyist gunsmith.  To the best of my knowledge, this has been restricted to mockups (Justin Halford used a stereolithography made frame to test component fit for his fantastic Beretta 92FS project) or less critical parts like furniture (grips, buttstocks and such). It wasn’t until I came across an AR-15 magazine follower on Thingiverse that I began to wonder about the feasibility of making more functional parts with a rapid prototyper.

The use of plastics in firearms is a relatively recent development as far as primary structural components go.  Firearms have certainly used plastics early on (the use of phenolic ‘Bakelite’ was popular for grips and other previously wood furniture in the years leading up to WWII and well afterwards), but use of plastics for a core component took much longer.  Consider a car analogy – we’ve seen plastic dashboards for many decades, but the use of plastic for something as critical as an engine block wasn’t attempted until the early 1980s.  It wasn’t until 1959 that Remington (at the time owned by DuPont, hence having access to cutting edge polymer technology) came out with a .22 rifle that used plastic for the receiver (the core ‘body’ of the gun).  This was the Nylon 66, so-called since the Zytel-101 material used was a type of Nylon 6-6 polymer.  While it was quite a popular rifle (selling over a million units by the time it was discontinued in 1991), and helped further the use of synthetic stocks among shooters, it wasn’t until Glock pistols became popular that polymer firearm frames/receivers gained widespread acceptance.  Today, polymer framed pistols outsell their metallic counterparts, and new rifle designs increasingly use molded synthetic receivers.

The AR-15 rifle, while designed to use an aluminum lower receiver, has such limited force imparted while firing that I guessed it could probably be made of printed plastic with little worry of breakage.  After all, Orion’s Hammer has successfully made a lower from HDPE (after having limited success making one from a pine board), not to mention the commercially produced polymer receivers such as Bushmaster’s Carbon 15 and Plum Crazy C-15. It would easily fit within the build volume of the Stratasys, but my concern was whether or not it would have enough precision for all features to be usable (Orion’s Hammer didn’t worry about the takedown pin detents or bolt catch, for example).  Rather than waste a lot of material on a failed idea, I took Justin Halford’s IGES file of the lower, scaled it to 75% of full size, and set it running with PP3DP filament.  The resulting print looked fantastic:

Figuring that my chances with a full scale print were excellent, I decided to modify the model by strengthening two areas that I was slightly concerned about – the front takedown pin lugs and the bolt hold catch lugs.  Adding more material to the model in SolidWorks was pretty straightforward, and I finished it up by adding an integral trigger guard.  I switched out the PP3DP filament for some black Bolson ABS – after all, the ‘black rifle’ would look a bit odd in ivory (more importantly, it’s easier to see/photograph detail on dark material).  After slicing the STL file, I sent it to the Stratasys and waited a few days (no speed demons, these old machines).

After breaking away all of the most easily removed support material, I had a great looking print.  I had generated the STL file at a very high resolution, as I was wondering how well the buffer tube screw threads would actually turn out (having not yet tried printing any threaded objects).  As it happened, perfect!  A buffer tube screwed right into the threads with no cleanup required.  Naturally, I wanted to share my results, but unfortunately firearms are presently a bit of a touchy subject.

The concept of using a 3D printer to manufacture gun parts has not been lost on the RepRap community, and the topic has been debated a number of times on the RepRap forums.  At this point, there is a policy proposal to not allow weapon designs or projects to be uploaded to the RepRap library, and a line on the Health and Safety page for the RepRap project states “the RepRap researchers will work actively to inhibit and to subvert the use of RepRap for weapons production” (emphasis mine).  On the other hand, Thingiverse once had a rule against weapons in their terms of service, but later removed that restriction.  Afterwards, the Thingiverse upload page still said “Please don’t upload weapons. The world has plenty of weapons already,” but I assumed that this text was not updated after the TOS was revised.

I decided to ask for clarification on the Thingiverse mailing list.  The phrase “kicking the hornets’ nest” aptly describes the resulting discussion, I think.  In the end, Zach ‘Hoeken’ Smith (one of the Thingiverse founders) weighed in and clarified that such content is allowed, though discouraged. Fair enough. Apparently someone had taken notice of the commotion, and three weeks later, there was an STL file of a lower receiver posted to Thingiverse in what could be described as a confrontational manner.  Since the cat was out of the bag, I decided to upload my own STL model, as I wanted to hear constructive feedback on how the version might be improved to better suit the current limitations of 3D printing.  Well, apparently the resulting ‘weapons on Thingiverse’ debate raged hard enough that in February the lawyers were unleashed upon the site’s Terms of Use, and now uploading any content that “…contributes to the creation of weapons…” is verboten. Although that policy doesn’t appear to be enforced, I suppose they could yank my uploads and kill my account at any time, hence I’m re-documenting my work here.  Enough rabble-rousing – back to the fun stuff.

I’m rather jealous of people who can print the lower receiver with soluble support, as clearing support material from small diameter holes is a bit of a pain.  I used a pin vise and an assortment of small diameter drill bits to clear out all the long cross drilled holes in the part, using Duke Snider’s receiver blueprint for dimension references.  With all traces of gray polystyrene eradicated, I set about cleaning up the larger holes, as they were ever so slightly undersized (better than being oversized).  I ran a 5/32″ drill bit through the holes for the trigger and hammer pins, and eagerly installed the fire control group.  The trigger and hammer  functioned flawlessly, with no slop apparent in the pins.  The selector lever was a bit of a tight fit, so I worked it back and forth perhaps a hundred times to break it in.  After tapping the 1/4-28 thread for the grip screw, I attached the grip, keeping the selector in place by virtue of its detent.  Similarly, the magazine catch was a bit of a tight fit, and I had to carefully work the part back and forth in the receiver to make sure that it would reliably retract under force from the magazine release spring.  I then ran a 1/4″ drill bit through the holes for the front and rear takedown pins.  Unfortunately, I heard a quiet snap when drilling out the front hole, and sure enough, there was a break between layers.

On the plus side, this confirmed my suspicion that the takedown lugs needed reinforcement in the first place.  I brushed on a bit of Weld-On 3 to fuse the layers together (delicately, recalling what happened when I dunked printed parts in MEK).  After running a drill bit through once more, the cleanup was complete, and I installed the takedown pin with its spring and detent.

Nice!  Now, for the other area that had given me concern – the bolt hold lugs.  Sure enough, when I pressed in the roll pin, I had layer separation.

Well, I never cared much for roll pins anyhow – they always seemed rather brutal (especially when driven into a blind hole – yikes).  After touching up the damage with a few more dabs of Weld-On 3, I ran a 3/32″ drill bit through the hole.  I then threw away the roll pin and instead used a dowel pin of the same size.

A little bit of superglue on either end of the pin should suffice to keep it in place.  Finally, there was the rear takedown pin to contend with.  Justin’s model appears to have the recess for the pin head as around 5/16″ or so, while the head on the pin from my DPMS parts kit measures 3/8″.  No worries – I lightly clamped the receiver in the mill vise, centered the spindle over the hole, and carefully widened the counterbore out with a 3/8″ endmill.

After this, the takedown pin fit perfectly.  Since I don’t actually have a full AR-15 stock (and will be attempting to run this receiver as a pistol first), I needed a way to capture the detent spring for the rear takedown pin.  I opted to tap 4-40 threads in the rear of the spring hole and kept the detent and spring in place with a 1/8″ long 4-40 set screw.  Unfortunately, the force on the detent was heavy enough that when I tried to slide the takedown pin into the receiver, the detent broke through the thin wall into the rear of the FCG area.  It appears that extra 1/8″ of spring compression due to the set screw may be too much.

I dabbed on a bit of ye olde Weld-On 3 and clipped 1/8″ off of the spring to compensate before attempting to secure the pin again, but the detent still wanted to break through the wall.  I’ll leave it out for the time being, but I’m considering drilling the hole out larger and sleeving it with brass tubing.

Overall, it’s looking quite promising.  The upper receiver fits snugly, and magazines can be inserted and removed with ease – shown is the lower with an upper attached along with a .22 magazine that I intend to use with the CMMG .22 conversion kit.

60 thoughts on “Gunsmithing with a 3D printer – Part 1

  1. Thanks, Pete – yep, I’ll be at the meetup on Sunday and was planning on bringing it, as it’s the most complex piece I’ve printed. Just yanked the head out of the Stratasys so I can have that as well (wish I could bring the whole machine, but I’d need a U-Haul truck).

  2. Where is this 3d Printing Meetup you and Pete were talking about? sounds interesting, chances are its not near me though…

    I printed my receiver sideways rather then up and down as you did, I m wondering if that will have an effect on layer separation, I m thinking it will strengthen the areas were you were having issues but will possible poss issues in new areas….

  3. The meetup was in Milwaukee:
    There’s going to be an even bigger event in Madison in a week and a half:

    I think you’re right about sideways printing and layer separation – I like printing the receiver vertically, as it ensures a nice clean magwell, but the front lugs certainly suffered. A sideways print would probably allow even unreinforced front lugs to hold up just fine. Unfortunately, the bolt hold lugs and detent hole for the rear takedown pin may suffer as a result. Seems application of solvent to critical areas is required no matter what, as you’re always going to have something affected by the anisotropic nature of the process.

    Maybe somebody could try printing a lower tipped at 45 degrees in two axes so that no holes are aligned with a printing axis? At least then all the holes should be equally resistant to layer separation.

  4. Tempting, its just a 2.5 hour ferry ride away… looks pretty cool though!! very neat place, I wish there was a place like that in West Michigan. I see there are a few in the east side of the state. thanks for the info, I ll let you know how my build goes. I also printed a 1911 frame for kicks. might work for a 22 conversion kit but I m not sure. I ll have to look into it more. glad to know the 22 kit works with the printed lower. do you think it will stand up to larger caliber rounds? I was thinking a 5.7 upper would be cool with pretty low recoil and stress on the lower… We need a forum for 3d printed gun parts and accessories… There has to be more of us out there sharing these same common interests….

  5. I’ve been thinking of printing a 1911 frame to use as a cutaway to show the internal operation, but I’m not sure about using it for a .22 – I guess I’d want to have a look at one of the commercial polymer 1911 frames to see where they actually added metal in order to strengthen the part. Having an AR-15 bolt carrier impact your shoulder from a failed print would be much more desirable than taking a 1911 slide in the face, so I’d certainly proceed with caution on that project. I’m also wondering about wear on the slide rails – definitely a lot of interesting things to consider with the design, certainly!

    I’ve looked at the 5.7 uppers as well, but that would be a lot of money to spend just to prove out a concept (unless you already own a PS90). I actually just got in another bare upper that I can attach my original DPMS .223 bull barrel to, as well as a buffer, buffer spring, etc. Again, I’ll test it all out with the aluminum lower first, and then switch to the printed lower for some cautious single-shot testing.

    Likewise, I was wondering what the best forum for 3D printed guns would be, as this is really a brand new field we’re forging… has had a little bit of discussion on 3D printing parts (and far more discussion of the legal aspects of doing so), but is more focused on the DIY machine-it-yourself aspects of gunsmithing. I’ll continue posting updates here on the blog, but I may start a thread or two elsewhere to see if there are any others interested in the intersection of gunsmithing and 3D printing.

  6. Seems like a shame that some websites prohibit or discourage making things like this. I know next to nothing about rapid prototyping and 3D printing, so I thought I’d ask: Are admonitions like the ones you mentioned the result of discussions within the community, and an attempt to prevent some feared scenario that might arise as a result of being able to 3D print weapons? Or is it just the result of individuals who are already uncomfortable with weapons in all contexts?

  7. Wow, excellent question! I think it’s generally a mix – you have a person or persons in charge who may be somewhat uncomfortable with weapons in general. On top of that, they may have concerns about legal liability regarding content posted on a site that they own/operate/maintain. Discussion within the communities does happen (and debate rages long and hard as I’ve discovered), but at the end of the day, it is up to the site owners/operators to determine what they consider to be allowed content. Online communities may appear to operate as democracies, but they are not truly so.

    Fortunately, as 3D printing (or any other technology for that matter) expands in usage and exposure, it will find its way to other communities that are not averse to its capabilities. Look to the printing press as a prior example – the Catholic church feared the spread of the technology, as it meant that access to (and interpretation of) “the word of God” was no longer in the hands of the clergy. Likewise, as 3D printers become commonplace, those championing the technology will have to come to terms with the fact that they cannot dictate its usage.

  8. Heya, boss! As I said, I’m surprised nobody seems to have done it before me. I’ll have to bring it along to a build party (assuming you’re still running them) – been wanting to do more with the various parts kits I have gathering dust. Plus, I’d love to watch you bump fire my Mateba again!

  9. wow, i would like to say that i will try this too, but i think this is a bit above my skill level. very nice work. now i am kind of wanting a 3d printer. there is no limit to what can be made.

  10. I know a little about firearms and my curiosity brought me to your site. Cool stuff! I’m rationalizing getting a printer…

    Anyway, on a regular 5.56 CMMG M4 LE, running the CMMG .22 conversion kit caused MORE stress on the hammer pins causing several to fail. This was a pre-Evolution model; CMMG acknowledged that the conversion kit added stress & recommended using KNS pins with external support. It seems counterintuitive that a .22 might produce more force on the lower than .223 / 5.56 – YMMV.

  11. Практиковался в чтении англоязычной литературы…спасибо, прочитал с интересом!

  12. I have printed up a number of paintball gun parts, actually! By gentlemen’s agreement, however, I can’t discuss them. I did print out hopper halves and a pump back in this post: I’ll have to revisit those parts again at some point with proper support material.

  13. Wicked !!!!!!!! You should make more types like snipers and shit . Seeing them printed would be really AWESOME. GREAT job!!!

  14. Hello i’m Matthieu Mas from France, i work for the artwork-management of the Biennale internationale du design de Saint Etienne France and we would be glad to show your work during our event please could you give me an email where i can send you some documentation ?
    I hope to read you soon !
    best regards Matthieu.

  15. This has got to be one of the most amazing developments in both the firearms and manufacturing realm I have ever seen…

    Very glad you posted this and I hope you continue with additional experimentation in this area!

  16. I believe Defense Distributed has re-posted the files at, and I recall hearing that the files were also available on The Pirate Bay. There are probably many other locations as well – it was a very popular file.

  17. Ok just to get me up to speed on this… I understand the “furniture” being printed from ABS plastic however with important stuff like the firing pin + Barrel + magazine, surely these aren’t printed and rather are purchased metal items?


  18. I didn’t print any of the furniture (though they could easily be made via that process). The barrel, magazine, bolt, etc. are all commercially manufactured metal parts, but the core component of the entire gun (the lower receiver, the part that is by itself legally a firearm) was 3D printed.

  19. Holes that are vertical to the table come out nice and round on the 3D printer, whereas the horizontal ones have stairsteps, and weaken the part (as you show in one picture). My thoughts on this is to print the lower without holes, and then print a drill jig to drill the holes out. You could make flat plates in the 3D printer with holes sized for drill bushings, butt it up against the reciever, and drill out with a had drill. Just my .02

  20. I don’t know too much about 3d printers or the types of plastics they can use, but from what I have seen so far the lowers fail after around 6 rounds. Do you know if anyone has looked into stronger plastics or composites? Would Celazole be able to feed through the printer?

  21. My lower has held up for 200-300 rounds of .22 and perhaps a dozen rounds of .223 (see parts 2 and 3 of ‘Gunsmithing with a 3D printer’), and remains intact and functional. The lower failing after 6 rounds you speak of was Defense Distributed’s first test using my design. DD used a lower printed on an Objet machine, and the photopolymer used has a relatively low impact strength (and the precision that the machine provides makes for some excellent crack propagation points). At some point I hope to try a lower made with a methyl methacrylate ABS for a slight strength improvement, though use of a fiber reinforced PC/ABS blend would be even better.

    PBI has such a high glass transition temperature that it cannot be fed through any currently existing FDM type printer. PPSF or PEI are about the extreme end of what is currently capable with the FDM process.

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