I have a semi-auto Uzi (clone) SBR with a 10.5 inch barrel. I built it from an Israeli parts kit and a fully welded Mckay receiver.

I'm not sure if this forum is the best spot to post this, if not someone please move it.

Recently I had: Failures to feed, failures to eject, and craters in primers.

After some research I:

-Adjusted top cover gap to roughly .010 (was around .022)
-Adjusted and cleaned extractor
-Polished feedramp and face of chamber with a Dremel and fine wet sandpaper

I took it to the range today, and it was still having some FTF at first. And a couple times it failed to strip a new round from the mag and I fired on an empty chamber.
Ammo used was Blazer Brass, PPU NATO pressure, Browning 147s, and steel cased Barnaul.

The FTF happens with multiple magazines, so I'm not sure if it's a mag issue. The round hits the side/top of the face of the chamber/barrel. It deforms the brass/copper jacket sometimes.
-Oddly, I seemed to get two different recoil impulses. One seemed soft, and the other seemed harder. Like the bolt was slamming back completely. I am using a thick black plastic recoil buffer.
-The PPU NATO pressure ammo got stuck in the chamber (second time) and it was a pain to get it out. After looking at some other spent brass, I have concluded that the firing pin protrudes too far off of the bolt face. There are large craters in some primers and literal holes in others (like the one that got stuck).

- Through the first few mags it would jam, regardless of ammo and magazine it seemed. The last few mags it ran perfect, even fed the flat nosed 147 grainers.


What the hell is going on?

Could it be:

-Recoil buffer too long/thick?
-Bad recoil spring?

And does anyone know the proper length that the firing pin should protrude so I can file it down?


I realize this is a lot of info, so thank you to anyone who responds. This thing is frustrating me lol.

Thanks for the help!!

Have you tried Uzi Talk forum?

Might be slightly out of alignment when welded.  Could be receiver feed ramp or both slightly not square.  I have noticed some new aftermarket barrels (sarco)  don't have a decent chamfer and this may also be a problem - snagging the projectile on the way in.  Might want to Try some gentle polishing on the barrel if it doesn't have a good smooth chamfer.  Uzitalk is good for asking questions.

I have a setup pretty much just like yours. You didn't mention what brand barrel you're running.
I have a Green Mountain 10.5" on mine and it runs like a top, although there have been people who have had to have the mouth of the chamber adjusted.
The chamfer was too sharp and the rounds would hang up on the corner as they tried to enter the chamber.

I got the barrel from RTG Parts.

I have century uzi that was doing the  same, except it was with a 16" barrel. I did all the the things that you have. I also needed to adjust the magazine catch tab. The magazines were sitting a little too low.
I would also suggest going to the uzi talk forums.

I'll try the Uzi Talk forums if it's still acting up after my next outing.

I think I fixed the punctured primers issue though. I filed down the firing pin and checked function by removing the bullets and powder from some 9mm cartridges and testing the ignition in my backyard. Lol.

They all went off, and no more cratering/punctures even on the NATO rounds. So that's good.

Hope I can fix the other stuff.

Since you built it from a full auto parts kit, did you use the full auto recoil spring?

That may be causing the fail to feed and fail to extract. The fully auto one is longer than a semi auto recoil spring. Too much forward pressure on the bolt.

I had a Sarco IMI receiver Uzi that was built by Vector. I was having the same problems and thought it was the top cover gap as well. Polished the top of the bolt and tried to loosen it up. Ended up being it just had the wrong recoil spring.

Edited to add:

Also, what grip housing are you using? A modified full auto to semi auto one? The semi and auto ones have different diameter grip housing pin holes. I want to say 5mm and 7mm. It’s been a few years, so I can’t remember which had 5mm and 7mm, but it the grip housing may be 2mm too low and couple with the wrong recoil spring it may be passing over rounds from the mag or not cycling the bolt far enough aft to pick up the next round.

I believe it is the full auto recoil spring. I'll try a semi-auto one.

The grip housing is an Israeli surplus that I converted to semi. The pin that goes through the grip/receiver fits fine, I'm not sure if that indicates anything though.

Swapping to the correct semi auto recoil spring should fix the issues you’re having then.

If it cycles with the new recoils spring you should be good to go. If it doesn’t run 100% I’d look into the grip housing and make sure it is fitted properly. If it’s too low the bolt can ride over the magazine and not strip a round out of it when cycling.

tag