This is a polymer clay magazine well block that adapts an AR-15 to use STEN magazines. This version is made from Sculpey III polymer clay and steel. I will be making a CAD drawing to post as well with my intention being that this can be 3D printed and built at home. I just ordered a 3D printer so I won't be able to test this for a few weeks.

It would seem simple enough to cast & bake.  I was thinking of using a pair of threaded steel rods interlocked as the ejector.  Bake it in the clay, then cut the tops down to fit.  Think that might work?

It might but having the flat stock seems pretty dang sturdy.

That's true.  Also seems like a bit more fab time for the Dremel.

I'm almost done with the CAD drawing. It will just use a 1/8x.5" piece of steel for the ejector and a 1/4x3/8" steel piece for the latch.

If you can, it would be helpful if you also publish it as a .pdf

Put 150 rounds into my 5 gallon sand bucket and barely see any wear on the block. I used the opportunity to test about 15 different STEN magazines that I converted back to 32 rounds from 20 rounds. All worked flawlessly. I then decided to pour a handful of sand into the open upper receiver to test reliability. I did not have one single malfunction the entire test session. I then spent an hour cleaning the damn gun of all the sand and powder residue from my dirty reloads.







Also I noticed a flaw with the New Frontier 9mm bolt, the "gas key" bolts are not staked, or even loctited. They loosened up after only 150 rounds. After completely cleaning the rifle I reinstalled the bolts with red loctite and tightened them as much as possible without stripping them, hopefully that will do it.

If not, you can stake them w/ a punch & hammer.

I should have checked them first but I foolishly assumed they red loctited them. Not a big deal, it still ran like a greased top. I'm very happy with this upper. I saved about $300 by building my own barrel and magblock and assembling everything myself, I'd highly recommend it. Now I'll need to hit the range to test for accuracy.

Love it.

Are you using any kind of depth stop for the magazine? I made one of those a while ago and had to flatten the dimples on the mags to get the correct depth to feed right. Bad idea I discovered. Mag can go in way too deep and stop the bolt. Ended up milling a "D" shaped notch on either side of the inside of the mag well to act as stops. All good then. No mods to magazines needed.

I actually thought milling a small flat on the magwell would be perfect, however I just barely flattened the dimples on the mags just enough to allow them to catch, having the flats on the magwell would be perfect though, but I didn't feel like permanently altering the lower if I didn't need to.