Gunsmithing with a 3D printer – Part 4

Well, to say that a lot has happened since Part 3 would be something of an understatement.  To recap:

Defense Distributed tried printing my AR lower STL on an Objet machine, but it only held up for 6 shots.  While much was made in the media about this ‘failure’, I thought it was actually an excellent demonstration of material properties in the two different 3D printing technologies used.  My FDM printed lower used material with a higher impact strength, while the Objet printed lower was stiffer.  As a result, mine flexed and would not cycle properly with .223 ammunition, while Defense Distributed’s lower cycled perfectly with 5.7x28mm ammunition, but fractured at the root of a buffer tube thread (interesting how the extreme detail afforded by the Objet process actually created stress risers due to the threads in my STL model being perfect ‘V’ profiles with no filleting of the thread roots).  They’ve since refined the model to hold up for 600+ rounds, which is quite impressive for a photopolymer.

Representative Steve Israel started calling for renewal of the Undetectable Firearms Act, and has also called for making 3D printed firearms and homebuilt ‘undetectable’ polymer magazines illegal.  I’m taking this somewhat personally, as he keeps using a giant photo of my AR lower as .22 pistol during his press conferences – the least he could do is put my URL on the photo to provide proper attribution.  Given that some of the most popular rifle magazines commercially made today are of polymer construction, I’m not sure what he’s really hoping to accomplish by expanding a law that was passed due to media hysteria over the introduction of the ‘plastic’ Glock pistol.  Wait, media hysteria over plastic guns?  The more things change, the more they stay the same…

After the horrific shooting in Connecticut, Thingiverse pulled almost all of the firearm related files, including my AR lower and a Magpul style trigger guard I had designed.  I immediately contacted their legal counsel and pointed out that a trigger guard is a rather important safety device and has use in paintball and airsoft, not just firearms.  The response was ‘our sandbox, our rules, and we can change the rules at any time’ (but spoken in far more lawyerly terms).  An AR-15 grip that had also been taken down was reinstated a few days later, so I’ve been asking how to get my trigger guard reinstated as well.  However, my requests appear to be ignored, and I’m somewhat giving up on Thingiverse at this point.  It’s still a great community, but when I can’t use it to share with other gunsmithing hobbyists or even paintball and airsoft enthusiasts, my desire to use it naturally diminishes.  Meanwhile, Thingiverse appears to have no issues with people sharing drug paraphernalia designs, so maybe they’re attempting to cater to a rather different group of ‘hobbyists’.

For anyone interested, I have a copy of my original AR lower STL here (though I don’t really recommend it at this point – there are much better 3D printable lowers that have been designed and refined by other folks).  I have a copy of the trigger guard here.  It comes in two versions – one is the standard version that uses a roll pin through the rear holes, and the other I designed to be a tool-free version that uses angled studs to snap into place.  I’m actually rather proud of this version, and would be happy to hear feedback on it.

Back to the present – I really haven’t done anything further with the printed AR lower, as I’ve been experimenting with a different firearm platform.  Commenter Allen had asked “Could the Ruger 10/22 receiver be built the same way?”  This certainly got me wondering, as the 10/22 receiver, unlike an AR-15 lower receiver, is what the barrel attaches to, and contains the reciprocating bolt.  Additionally, the fire control group (trigger, hammer, etc.) is contained in a modular pack rather than having those components fitted individually to the receiver.  Plus, answering this question seemed like an excellent excuse to finally purchase a 10/22 – like the AR-15, it’s an incredibly popular rifle with countless aftermarket accessories available.  Additionally, it’s a great platform to learn the fundamentals of proper marksmanship (one of the many skills that I’d like to learn one of these days).

I found a very well used one at Gander Mountain for a reasonable price – the sling swivels had apparently broken off long ago and the receiver finish was a bit worn, but it looked to be in good functional order and would do well for learning how the rifle operates and is constructed.  When I got it home, I eagerly dug into the disassembly to see how it functioned and to give it a much needed cleaning.  The 10/22 is a semiautomatic, blowback operated .22 rifle.  The blowback operation means that unlike the AR-15, the bolt is not locked into place when the gun is fired and is only kept forward by means of the recoil spring.  A blowback bolt is also quite heavy in comparison to the cartridge used – this is to ensure that the bolt begins its rearward travel in the firing cycle slowly enough to let the chamber pressure decrease to a safe level before the spent cartridge is extracted.  The receiver itself is cast, though there are aftermarket billet receivers available for those looking to heavily customize the rifle.  In looking at how the bolt reciprocates in the receiver, it appeared that there should be no issues with a 3D printed receiver, provided that the print is made so that the layers are parallel to the barrel axis (to provide as smooth a surface as possible for the bolt’s travel).

For the printed receiver itself, I again turned to Justin Halford’s cncguns.com for an IGES file.  Unlike the AR-15 lower receiver, there weren’t any design features that I felt needed strengthening right away, so I created an STL file directly from the solid model and set it running with the same Bolson black ABS I had used for the AR lower.  I printed the receiver upside down so that the interior didn’t need any support material, and thus would provide as good a finish as possible.

After removing all evidence of support material, it was time to start fitting parts.  Chief among these is the barrel itself, but the hole in the receiver was slightly undersized (not unexpected, and better than being oversized).  I clamped it to the angle plate on the mill and indicated it in vertically with a dial indicator and coaxially with a Blake co-ax indicator before opening up the hole with the boring head.

After bringing the hole to appropriate size (I could just begin to insert the barrel shank), I tapped the barrel clamp holes with 12-24 threads (thanks to the blueprints at fireamfiles.com) as well as the stock mounting screw hole in the front tang.

Next was to actually test installation of the barrel itself, which tightened up nicely, but I noticed that the barrel would visibly cant downward as I tightened the clamp screws.

After removing the barrel, I saw that there wasn’t quite enough clearance on the front counterbore, and the back of the barrel was catching on the top front edge of the receiver.  So it was back to the boring head to enlarge the diameter on the mating face slightly.

Then, it was time for a test fit of the bolt – it was a tight squeeze to get it past the rail on the inside right of the receiver.

As it turned out, I think the rear wall of the receiver in the original IGES file may be a touch too thick, as I also couldn’t get the trigger pack installed, so I thinned out the rear by perhaps 0.030″ until I could just get the retainer pins to go through the receiver and trigger pack (I had already reamed out the holes in the receiver at this point).

With that done, I could finally fit all the internals and actually dry fire the gun.

However, when I tried to drop the receiver assembly into the wood stock, it wouldn’t fully seat.  After fumbling with it for a few minutes, I noticed that there is an extra relief cut on the original receiver at the interface between the tang and the receiver front.  As it turned out, the original IGES file does indeed have this relief cut, but when I brought it into SolidWorks, I had run a feature recognition pass on the part.  For some reason, SolidWorks removed this feature – I should have just done a direct export to an STL file instead!  Oh well, one last machining pass on the mill took care of it.

The barreled action fit just fine in the stock, and both the 10 and 25 round Ruger magazines fit, though perhaps a little more loosely than desired.

Today I took it to the range and found an accomplice to act as a model.  Naturally, I let him burn through some rounds on the 3D printed AR receiver configured as .22 pistol first.  A .22 AR pistol is kind of a ridiculous contraption, but it is also ridiculously fun.

Next was the test of the printed 10/22 receiver.  As with previous testing, I started with only 1 round in the magazine and worked my way up.  Things were running just fine, so I put in the 25 round magazine and let ‘Secret Agent Man’ have some trigger time with it.

Generally, it ran nicely, though we did have some feed issues with it.  I think the fitment of the magazine could be to blame, as it seems that the front of the magazine is able to tip down a little too far.  Both magazines are also absolutely brand new (this was their first usage), and I’ve been told that 10/22 magazines operate better after an initial break-in period.

So there you have it – a 3D printed 10/22 receiver is entirely feasible!