DefDist Printed AR Mag - Part I

This is a review of Defense Distributed’s first printed 30 round AR magazine.

In the interest of time and Liberty, you can already download our working files for the piece over at DEFCAD. Now, let’s talk about how this guy performed today. 

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To test printable hicap mags, one must first journey to the heart of the fledgling neo-confederacy. 

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Once there, walk west until you hear a stranger say the word “secede” in conversation (Difficulty: Easy).

This magazine was designed in a four day period and printed in 7:30 on an Objet connex260. Material is VeroClear- we thought it would be wise to demonstrate both a round count and feeding in action. The magazine was designed to use a follower and floor plate already designed by crank, and hosted at DEFCAD (crank’s 10 round magazine is by far the most popular download on the site). We now host separate follower and floor plate files for each magazine, however. Download what you like.

Anyway-

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Function and position checks. The mag catch slot seemed a little larger than a pmag’s, and there was some noticeable play in the well. We began thinking the magazine’s lips were a problem area around this point. Look at the corners….

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And smooth feeding was not to be in the cards. We had to break out the blades (and keys) to shave practically every component at least once. Note the lip and rail thicknesses below, these would be substantially changed about three times. 

Our first hour of testing was a bunch of one-shot strings of fire. The bolt would catch the first round and fire, but successive rounds would jam in the feed ramp. A number of factors were contributing to this cycling problem, but the biggest seemed to be that the rounds were set too low for a good catch.

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The picture below was taken after our second misfire, when we began carving in earnest around the top of the piece. The corners had to go. The follower wasn’t moving freely enough in the magazine body either, and it took a good 30 minutes of patient shaving to get that ironed out.

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Reference and replacement pieces. These floating boxes are invaluable when performing magazine surgery.

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After enough carving and reloading (yes, upside down), we thought we were in the clear for a solid string of fire.

Test Fire

I can see now that I should have been clearer, but there was no failure in today’s test. What we see in the video is not the piece breaking or becoming unusable. The mag would later crack and take the beaten appearance you can see at the beginning of this blog post, but it is still “usable” if you’re into terrible magazines that only work 3 to 5 rounds at a time.

I get that that’s our thing now though. Defense Distributed prints and breaks guns. Not quite today, however. Our problem instead looked like this:

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With these rounds (and we tested both .223 and a slightly longer PMC 5.56) set as they were, the bolt would nick the back and slice the side of the cartridge.

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This still involves quite a bit of force. The bullet was punched into the casing you see above, sending powder generally everywhere inside the upper receiver and the magazine.

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With each jam we’d usually get a punched in round and would have to set to cleaning before modifying the piece, rebuilding, and making another attempt at firing.

After about three hours, and with fading daylight, we had to abandon our printable hicap field hospital. We fired 12 total rounds through the piece, but the largest sustained string of fire was five rounds.

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Before heading back to Austin, we stopped for sage advice.

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Ideas for Improvement

There is a lot to mention here, and I really must to bed, but we’re going right back at this again today with a new piece and better reference measurements. 

After getting back into town, we were able to make today’s magazine cycle 20+ times with a little graphite, a lower than milspec feed ramp, and still more cylindrically carved feed lips.

Getting close.

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