DefDist Printed AR Mag - Part II

Test Fire

That needed to come first today.

So, Saturday began with meeting back and comparing notes. Yesterday’s mag was fitted and cycled in different pre-grandfathered (just kidding, no one out here is going to do that) ARs. After Friday evening’s tests, we added graphite inside the mag body to make feeding as smooth as possible.

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We ran the bolt on some dummy rounds and were again able to run 15 rounds through the piece, but the lips were cracked, and after breaking out some digital calipers we confirmed that the mag catch slot was just too high compared to other magazines. This was Friday’s major problem.

Friday’s mag was seated 1.75 mm too low. Our design took features from another piece already hosted at DEFCAD, one by crank and mentioned previously. Friday, we were out on the range cutting on the Objet mag with keys and a knife to get the piece working. Saturday, we broke out an identical piece to the previous one printed in an epoxy-based SLA resin (qualities near identical to ABS) and set to making modifications again from scratch with better tools and measurements. 

Importantly, ***The current CAD files at DEFCAD do not yet reflect Saturday’s modifcations.*** Both DEFCAD AR mag IGS and STL files will be updated within 48 hours to reflect the changes we made this weekend.

Those changes were essentially these: 

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We added 1.75 mm of material to the top of the mag catch slot, and subtracted the same amount from the bottom. The mag would now sit higher out of the well and into the chamber. The consequence is that now your feed lips come a bit too high and will be snagged by the bolt without some filing. So we took a flat file and gently lowered the lips until the bolt cleared without incident.

Cylindrical filing was also still in order for the inside of the feed lips. The current IGS and STLs in both 10 and 30 round feature lips that are too angular and thick- and though thickness is understandable, the shape needs to taper more for a reliable feed up the ramp.

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Here you see sanding of the piece after modifications were made to the mag catch slot.

We introduced a little graphite into the new mag body, and after some cycling, we felt confident grabbing Friday’s follower and floor plate and heading back to the range for some failure testing.

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The piece after running about 50 rounds through it. Over half of that on auto. That bolt is hot, and you can just see the plastic of the lips beginning to deform.

Below is the best picture we’ve got to show how we also lowered the front follower rails. This may not be absolutely necessary, but we found it greatly helped the angle of the round out of the mag on Friday, and so we duplicated the modification with the new piece. This change will be included in the CAD updates.

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The following images were taken after we fired every round of .223 we had with us. Final count was 85. Yes, that’s 5.56 in the background, but we were content with testing and opted not to use it. We only gave ourselves an hour of daylight at the range for proof of concept.

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Our follower had some shaving done as well, and we will probably include a modified follower IGS file with the mag body update.

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The lips were starting to move up from the heat, but it would work well past 100 rounds.

So back to the software. Stay tuned for some AK mag variants.

Oh, and here’s something to keep the prohibitionists up.

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*Clicks Print*

  1. victorcrespo reblogged this from defdist
  2. clems-ramblings reblogged this from defdist and added:
    its finest. Great pics included. Worth going through.
  3. bullit1987 reblogged this from defdist
  4. raidokaos reblogged this from defdist
  5. kasaron reblogged this from defdist
  6. annerajb reblogged this from defdist and added:
    printed gun parts yay.
  7. hewhositsinthedark reblogged this from defdist