Interesting malfunction, possibly solved

Garrett

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So I had had an interesting failure. Or rather, I may have figured out a long-ish running issue I’ve been having. I have been experiencing multiple failures to feed for a while now. This is on a F/A gun completed by Group Industries (pre-Vector).

I don’t think it has been an issue of weak ammo, as the failures usually happen on the first shot of a burst. So it’s like the cartridge was having trouble initially getting stripped from the magazine. I would get the cartridge part way into the chamber, but stopping part way in. But to take the ammo out of the equation, I have been using FMJ-RN 124 gr. NATO ammo from Igman. I haven’t run it over the Chrono yet, but it seems like the gun runs faster with it than with typical ammo.

I thought maybe it was due to tired surplus mags, but I bought some new Uzi Pro mags and still had the same issue.

So when I pull the trigger, I will occasionally get one that doesn’t feed all the way into the chamber. It isn’t nose-diving into the bottom of the barrel. Rather, the bullet is started into the chamber but gets hung up at an angle, with the bolt part way forward. The gun has a BWE feedramp, installed by Richard Hoffman.

rg9oIzp.jpeg


I had been shooting a surplus military barrel with the typical chamber, with the typical end prep. I switched to the original Group Industries barrel, which has a bit more of a funnel profile at the chamber end, but the issue continued.

Looking closely at several of the malfunctions, the cartridge case head seems to go about half way up the lower lip on the breech face and would hang up there. It kind of looked like the rim was getting caught on the cutout for the ejector. Examining the bolt breech face, I don’t see anything that appears to be out of spec. I was using a surplus military bolt that I’d gotten from somewhere. It was either a surplus bolt I had gotten from BWE, or it could have been an IMI bolt that came with with an Izzy parts kit I have.

LJXsCMg.jpeg


In any event, I swapped one surplus bolt for another and suddenly the gun ran flawlessly. For several magazines. I did not have a timer with me to check rate of fire, but the gun felt like it was running faster as well. I may have to clock the two bolts and see if there is a measurable difference in ROF. I may also try using a stone to round the edges on the ejector cutout. Although as noted, I don’t see any real difference between this one and any of my other bolts.

Kind of strange. Anyone else ever run into an issue like this?
 

Roaster72

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How strange. From your description I was certain it had to do with mag height or maybe top cover gap. Perchance have you looked at the ejector channel on the bad bolt? Was it hanging and slowing when traveling over the ejector?

Did the bad bolt always have the problem or was it fine and problems started later?

I have to admit, I'm a bit perplexed how a bolt change cured the problem.
 

Chef

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Have you tried swapping ejectors?

Do you mean the extractor?
Changing the ejector would require drilling out the rivet holding it in place and re-riveting a new ejector properly in place.
Not something most people would want to do unless completely necessary.
 

hacker

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I had the same problem when I got my Uzi 6 years ago. It is an IMI model A with the blocking bar removed, but restrictor ring left in place. It was only shot once each by the previous two owners, so it was like new. Jams just like yours on every mag when I got it. Did the top cover adjustment and tried different mags with no difference.

After about 1000 rounds it ran better but still had a jam every mag or two. I called Richard at BWE to get on his list to sort it out. He mentioned that I had a Group bolt (G on the side) and they were all warped. He said most GI Uzi problems were due to the GI bolts. I had plenty of other bolts but not clearanced for the restrictor ring. Richard said to send him an IMI bolt to him to clearence.

When I received the bolt back, it has worked 100% since then. I also noticed when I replaced it that the ejector was a little loose and peened the rivet down. My son was in college for mechanical engineering and he did a study on the bolt. Under high magnification photography you could see the ejector channel in the bolt wave from side to side. Warped like Richard said. That friction caused the issues. It also ran better after 1000 rounds because it loosened the ejector so it could move from side to side in the warped channel.

Richard told me that the warping was due to cooling too fast after annealing. That thin metal along the channel would cool down far faster than the rest of the bolt. Maybe the same issue happened to your bolt. Check to make sure your ejector has not loosened up like mine did from running the warped bolt.
 

Garrett

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Interesting. I have checked the ejector and it appears to be tight. I had swapped out the Group bolt that came with the gun several years ago.

Where replacing the bolt seems to have fixed the issue, there may be something similar to your issue with the ejector channel on the problem bolt not being straight.
 

amphibian

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Do you mean the extractor?
Changing the ejector would require drilling out the rivet holding it in place and re-riveting a new ejector properly in place.
Not something most people would want to do unless completely necessary.
Yeah...sorry, meant extractor...had the CMMG RDB on the brain.
 

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