Uzi Feed Issue: Help

PA2A

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Hello everyone,

I've been running into an issue with a post sample Uzi that I recently had built. The gun will run fine when I load 5-6 rounds into a magazine, but won't feed rounds when I load a full magazine into the gun. On the off chance that it DOES chamber a round, it will always give me a light primer strike (when a full magazine is inserted). Can anyone help me identify the problem?

Top cover is not too tight, the bolt moves freely with the recoil spring out and safety/trigger held in.
 

ericthered

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Is this a open bolt or closed bolt gun? Did the manufacturer weld it together or was it converted from a semi auto? And what ammunition were you using?
I probably wont be much help on this, but hopefully if you can provide a little more information on the gun, then the guys that know something can help you out.
After admitting im probably clueless, and until a more knowledgeable person chimes in, my guess would be a angled/out of spec trunnion. My theory is that if the trunnion is out of spec (up, down, left, or right) it is causing to much drag while chambering/straightening the round plus seating onto the bolt face. The lightly loaded magazine takes less effort to strip rounds from, so maintains more bolt velocity/energy necessary to still operate in less then ideal conditions. Wheras the full mag takes more effort to strip rounds which slows the bolt past the thin operational line of this particular gun.
If my guess is in fact the case, the gun "may" run "fine" with hotter ammunition. Which obviously isn't a cure.
 

delta-10

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I ran into this exact issue when trying out my Vector mini uzi with one of the new Barrel Exchange heavy bolts. I was pulling whats left of my hair out trying to figure out what the problem was. It turns out, I had multiple issues. The 1st problem I found was that a barrel I bought from Vector recently was chambered too deep. Primer strikes were very light to non existent with both open & closed bolt assemblies. Thankfully I had a couple other barrels to compare this one to and I thought that was the end of my problems.

Next range trip I put a good barrel in and it ran like a scalded dog with my closed fire bolt that I had bought from Amphibian off of GB. That proved that the gun was capable of running. Next up was the heavy bolt. I would get a few short bursts then a light strike. I would have at last 2 or 3 malfunctions per 32rd mag. I then remembered that I put in a Sarco extractor in the heavy bolt so I thought it was an extractor issue. I swapped extractors with the known good IMI one in the other bolt I had and no joy. I ran the Sarco extractor in the closed bolt and it ran with no problems so that ruled out the extractor being the problem.

One thing that I did notice is that when I would have a cartridge that wouldn't fire, it was really difficult to cock the gun and extract the unfired case. I didn't think much of it at the range and just finished out my day with the closed fire bolt that had the Sarco extractor in it. When I got home I took the gun down and gave it a through cleaning. I would take a bullet and would put it in the barrel and it would go in easily and fall out if the muzzle was pointed towards the ceiling. No sticky chamber. Next I took a dummy round that I made up with no primer in it and put it on the face of the bolt with the extractor claw in the groove helping to hold in in place (no recoil spring was installed so I could move it back and forth by finger pressure to see if there were any tight spots that might be causing bolt drag ) I noticed that when the bullet was on the face of the bolt that it required a bit of force to get the bolt to seat the cartridge completely in the chamber.

Ah ha, I have found the issue. The difficulty in chambering the round took just enough momentum away from the bolt so there wasn't enough energy left to set off the primer. This wasn't a problem with the closed bolt because the momentum of the bolt was enough to "hammer" the bullet home and the striker wouldn't "trip" completely until the bolt was closed.

My gun has the semi-auto ring in it and that was ever so slightly out of alignment. I was able to take a punch and tap the restrictor ring assembly with the barrel in it up a couple thousandths and now the bolt would easily chamber a round and there was no drag on extraction. My barrels were now easier to install and remove whereas before they were very tight.

Next range trip the gun ran perfectly. I was so proud of myself for being able to diagnose and fix my slightly out of spec Vector host. I was so afraid that I got a bad/out of spec bolt from Barrel Exchange. That was the only other thing I could think of. Thankfully that wasn't the case and now I have a mini-uzi that is dead nuts reliable just like my full size IMI.

Thanks again Troy for making another run of those bolts. Now I eagerly await your email for the barrel run. Please take more of my $$$$$ :)

Note:
I would normally not beat on a gun but saw one of Richard Hoffman's - BWE Firearms Youtube clips where he would give a gun a good whack or two to get a trunion back into alignment. He did bring up a good point in that these are just stamped steel guns and that they do flex and can be bent slightly and come out of alignment or be bent back into alignment if they were not built right to begin with.

Hopefully my story will help someone else get their gun back running right..........
 
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PA2A

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Is this a open bolt or closed bolt gun? Did the manufacturer weld it together or was it converted from a semi auto? And what ammunition were you using?
I probably wont be much help on this, but hopefully if you can provide a little more information on the gun, then the guys that know something can help you out.
After admitting im probably clueless, and until a more knowledgeable person chimes in, my guess would be a angled/out of spec trunnion. My theory is that if the trunnion is out of spec (up, down, left, or right) it is causing to much drag while chambering/straightening the round plus seating onto the bolt face. The lightly loaded magazine takes less effort to strip rounds from, so maintains more bolt velocity/energy necessary to still operate in less then ideal conditions. Wheras the full mag takes more effort to strip rounds which slows the bolt past the thin operational line of this particular gun.
If my guess is in fact the case, the gun "may" run "fine" with hotter ammunition. Which obviously isn't a cure.
This is an open bolt gun rewelded. Using Blazer brass cased ammo. Going to swap barrels and recoil spring today to make sure those aren't the issue.
 

root

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Since it's a reweld also check that the trunnion is set right.
I've seen two UZI guns in my life not feed or fire or feed only from one side from the front trunnion being to far forward.

One a McKay 30K to far forward wouldn't go bang but fed.

One reweld parts kit just over 50k to far forward gun only fed off the right side.

And my mini uzi build that the feed ramp I welded in was to far forward.
It was another that would only feed from one side ( I forget what side)
My home build was just grind and reweld to correct location of the ramp.
That was a Group Industries shell build.

It wasn't set to far off forward to notice with the eye but was enough to take a few days to finally figure it out.
 

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