Lightning cuts in a full size UZI trunnion.

[Chef]

Considering the full size UZI is a little on the heavy side, I'm wondering if making some lightning cuts in the trunnion would help. (before the trunnion is welded into the shell)
I noticed the mini has a lightened trunnion and thought that milling out some of that material in the same way as the mini might shed some ounces from the UZI.
Has anyone tried it before or is there any reason it wouldn't be a good idea?

 

[slimshady]

Should work fine, the Mini uses the same trunnion with the extra cuts and with a higher rate of fire. A semi puts a lot less stress on things. I just wonder how much the mini cuts drop the weight? The bolt is a boat anchor, I wonder if some lightening cuts there might yield a higher return on investment, assuming you kept enough weight to keep the bolt closed during firing. What does the mini bolt weigh, that would seem to be the lower end that is proven safe.

 

[Chef]

My UZI is a FA one (transferable model A RR, no blocking bar) and I'm having a lot of trouble with it properly operating. Regardless of the ammo type I try, I get at best, 5 rounds before a jam. After tinkering with it, I'm almost to the point of replacing the trunnion in it. Before I weld in a donor from a parts kit, I thought about milling it out like the mini to shed some weight.
Lightning a bolt is a future project I've been considering as well but only after I get the UZI to run reliably with the bolt in it's original configuration.

 

[bigu2fan]

My UZI is a FA one (transferable model A RR, no blocking bar) and I'm having a lot of trouble with it properly operating. Regardless of the ammo type I try, I get at best, 5 rounds before a jam. After tinkering with it, I'm almost to the point of replacing the trunnion in it. Before I weld in a donor from a parts kit, I thought about milling it out like the mini to shed some weight.
Lightning a bolt is a future project I've been considering as well but only after I get the UZI to run reliably with the bolt in it's original configuration.

Chef:

If your gun is a factory IMI A model that was converted by removing the blocking bar, I would say you have a very desirable conversion. I think it is unlikely a misaligned trunion is the issue.

Here are some questions that could help with troubleshooting:
1. Who did the conversion?
2. Is the barrel restrictor ring still in place?
3. If so, are you certain the bolt has been properly "clearanced" to fit over the restrictor ring?
4. If Group Industries did the conversion, they may have supplied their own Group manufactured bolt. These bolts have a reputation for causing big reliability problems. Often the solution is to get a surplus IMI parts kit bolt, have it properly "clearanced" to fit over the restrictor ring and your gun will run forever.

Again, I would find it VERY unlikely that on a factory IMI semi that was converted to full auto that the trunion would be misaligned.

There are lots of knowledgeable people on here that will help trouble shoot your Uzi. Can you provide some more info first?

--bigu2fan

 

[Chef]

Chef:

If your gun is a factory IMI A model that was converted by removing the blocking bar, I would say you have a very desirable conversion. I think it is unlikely a misaligned trunion is the issue.

Here are some questions that could help with troubleshooting:
1. Who did the conversion?
2. Is the barrel restrictor ring still in place?
3. If so, are you certain the bolt has been properly "clearanced" to fit over the restrictor ring?
4. If Group Industries did the conversion, they may have supplied their own Group manufactured bolt. These bolts have a reputation for causing big reliability problems. Often the solution is to get a surplus IMI parts kit bolt, have it properly "clearanced" to fit over the restrictor ring and your gun will run forever.

Again, I would find it VERY unlikely that on a factory IMI semi that was converted to full auto that the trunion would be misaligned.

There are lots of knowledgeable people on here that will help trouble shoot your Uzi. Can you provide some more info first?

--bigu2fan

It's a Fleming conversion.
Barrel restrictor ring has been removed from the original feed ramp.
I have two bolts, both IMI surplus from parts kits.

When I got it, it was in it's original configuration as it came from Fleming. It had a bolt that was clearanced for the feed ramp with it's restrictor ring intact and the trunnion was still sized for semi barrels. The bolt was, I think, a Group bolt as it had a "G" on it if I remember correctly.
Since it had it's blocking bar removed as part of it's original conversion, I thought it best to bring the rest up to SMG spec but after completing that, it wouldn't function correctly.
I have multiple SMG barrels that I tried swapping, both IMI and new Belgian ones as well as two different IMI bolts.
I have a few 9mm dummy rounds (reloaded cases without powder or primers but with a projectile crimped in place) as well as some snap caps that I use for function testing and when I am cycling the action, they often seem to hang up as they try to enter the chamber. Most often the bullet tip stops on the right (ejection port) side of the chamber instead of sliding smoothly in and that causes the bolt to stop. When I am actually firing it, (and I can get more than 2 rounds to fire in one burst) I can hear the cyclic rate is not steady, and I suspect the bolt is having issues pushing the rounds into the chamber and hanging up for a split instant before the force of the bolt convinces the round to seat properly and fire.
When I look at it from a top down view with the top cover and bolt removed, everything looks aligned, but I don't have the tools to measure it precisely.
Before I replace the trunnion, I'm going to replace the feed ramp as that's much easier to remove and square up prior to welding it in place. But if I do have to replace the trunnion, I will probably mill out some material to replicate the mini trunnion just for the weight savings.

 

[bigu2fan]

It's a Fleming conversion.
Barrel restrictor ring has been removed from the original feed ramp.
I have two bolts, both IMI surplus from parts kits.

When I got it, it was in it's original configuration as it came from Fleming. It had a bolt that was clearanced for the feed ramp with it's restrictor ring intact and the trunnion was still sized for semi barrels. The bolt was, I think, a Group bolt as it had a "G" on it if I remember correctly.
Since it had it's blocking bar removed as part of it's original conversion, I thought it best to bring the rest up to SMG spec but after completing that, it wouldn't function correctly.
I have multiple SMG barrels that I tried swapping, both IMI and new Belgian ones as well as two different IMI bolts.
I have a few 9mm dummy rounds (reloaded cases without powder or primers but with a projectile crimped in place) as well as some snap caps that I use for function testing and when I am cycling the action, they often seem to hang up as they try to enter the chamber. Most often the bullet tip stops on the right (ejection port) side of the chamber instead of sliding smoothly in and that causes the bolt to stop. When I am actually firing it, (and I can get more than 2 rounds to fire in one burst) I can hear the cyclic rate is not steady, and I suspect the bolt is having issues pushing the rounds into the chamber and hanging up for a split instant before the force of the bolt convinces the round to seat properly and fire.
When I look at it from a top down view with the top cover and bolt removed, everything looks aligned, but I don't have the tools to measure it precisely.
Before I replace the trunnion, I'm going to replace the feed ramp as that's much easier to remove and square up prior to welding it in place. But if I do have to replace the trunnion, I will probably mill out some material to replicate the mini trunnion just for the weight savings.

Oof! Well, is it possible that the trunion was not bored out correctly when “opened up” for SMG barrels? That is the only thing I can think of, given the information you provided. If the trunion was bored out such that the barrel is now no longer completely parallel with the receiver and thus the bolt then that might cause issues. Have you Taken the recoil spring out and Slid the bolt back and forth to examine how the bolt face and barrel interface? This might Help reveal Whether there are any alignment issues.

Perhaps that could shed some light on things? Maybe someone else more knowledgeable than me will chime in.