Modifications to Uzi Promag 3D Printed Mag Adapters

[nchunter182]

Wanted to pass along a modification I'm working on to hopefully resolve an issue I found. Last summer during a range day, I had 5 fully loaded mags sitting out on the table under the hot Texas sun. They ran fine at first, then I started to get a failure to feed. Discovered that the mag spring pushing the rounds up against the closed bolt was causing the adapter sleeve to slide up the mag and not presenting the next round in the proper place for the bolt to strip it. Pushed the adapter down to the stop on the mag but it would not stay in place when under spring tension. The heat had caused the adapter to lose its grip on the mag. I like the mag adapters so started thinking about a way to fix it.

Fast forward to today and here's what I'm trying. The adapter needs something better than a slip fit to keep it in place when it gets warm. I also was concerned about the mag catch hole on the adapter getting distorted and worn since it has to support the mag spring load. Decided the best way was to epoxy the adapter in place. I also made an aluminum bushing to insert into the adapter mag catch hole to bear the spring load and provide wear resistance. The bushing is epoxied in place against both the adapter and on the mag itself.

I decided on JB Weld Plastic Bonder epoxy to hold everything in place and 3/8"x.065" 2024 aluminum tubing for the bushing - all purchased from McMaster-Carr. Roughed up the mag bonding surfaces under the mag adapter, taped off the holes on the inside of the mag under the adapter to keep out epoxy from getting inside the mag (disassembly required), and degreased mating surfaces. Drilled out the mag catch hole on the mag adapter to 3/8" and cut the tubing to .275" lengths for the bushings. I had to hone out the inside of the tubing to .250" to fit the mag catch pin. Used a Dremel with a small diameter stone to accomplish this.

Coated mag adapter inside with epoxy and placed epoxy on the mag on areas I roughed up. Slid the adapter in place and used denatured alcohol for cleanup. Then applied epoxy into the drilled out bushing hole on the adapter and inserted bushing till it was flush with the adapter.

Here are some pics of the products I used and one finished mag. Hopefully get a good weather day this weekend to try it out. Will update with the results. I believe it is going to work well but now replacing the adapter is not going to be fun. Hopefully with these mods they will last for a very long time.

 

Jay

 

[nchunter182]

Well... no pics. I must not have enough posts yet.

[ron_brock]

Jay,

 

You should be able to post pics. Make sure to click on more reply options, type your message, choose your file to attach, once loaded, click attach this file and it should show up in your text above. When posted it should show. If you struggle with it, PM me and Ill send an email address to send and I can post for you.

 

Thanks,

Ron

[nchunter182]

OK, let's try this again.

Yep - looks like I wasn't following all the steps correctly.

Thanks Ron!

[nchunter182]

Today I completed all 5 mags I have. Weather here is looking great for tomorrow so headed to the range. Not supposed to be even close to the temperatures we saw last summer but I plan on leaving a fully loaded mag sitting in the gun for a while to test it out and see if the adapter moves. I suspect it's not going anywhere without a hammer and a chisel!

Will update.

[heavy artillery]

Interested to hear the outcome of your testing. I haven't personally experienced any loosening, but I do applaud your improvement ideas and effort.

[nchunter182]

Heavy Artillery - thanks! Just trying to keep it reliable and I enjoy working on these type of things..

 

Yesterday really wasn't a very good test. Last summer temps were mid 90's and just miserable hot/humid. Typical southeast Texas summer weather. Yesterday was barely upper 60's so had no issues with the mag adapters - they functioned as they should. I did run into a feeding issue that I didn't have before. When trying to chamber the first round out of the magazine, the round would pop up nose high and hit the upper end of the barrel causing a failure to feed. Checking them against my factory mag, that runs perfectly, I can see that the rounds are being presented a little nose high. Will move the forward feed lips in slightly to match the round angle of the factory mag and try again. I also noticed that the spring pressure on the Promag is quite a bit stronger than the factory mag. May be contributing to the round popping up a little higher. Maybe nothing other than the springs in them aren't 80 years old either...