What is the slowest 9mm round that will cycle a FA UZI?

Dirk Hawthorne

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Anyone ever try to see what the smallest amount of powder will cycle an UZI with 124 grain bullets and an MG sized suppressor?

I was thinking about trying it with Winchester 231 powder. Just wondering what velocity would be a good starting point.

All I got is 124 gr conical point lead heads right now.

My threaded barrel is one of those KAK FBI barrels, 8.5 inch
 

Hiller

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Anyone ever try to see what the smallest amount of powder will cycle an UZI with 124 grain bullets and an MG sized suppressor?

I was thinking about trying it with Winchester 231 powder. Just wondering what velocity would be a good starting point.

All I got is 124 gr conical point lead heads right now.

My threaded barrel is one of those KAK FBI barrels, 8.5 inch
By attempting this you will be creating a runaway machine gun at some point. With a low enough power charge the weapon will still cycle, just not enough to allow the sear to catch the bolt. Please use caution.



R/s, Hiller…….
 

Dirk Hawthorne

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By attempting this you will be creating a runaway machine gun at some point. With a low enough power charge the weapon will still cycle, just not enough to allow the sear to catch the bolt. Please use caution.



R/s, Hiller…….

That's a very good point. I had a 9mm MAC10 do a runaway on Remington 115 gr.

Remington UMC is probably the lowest powered ammo.

I suppose that if you got down low enough, you might leave a bullet stuck in the bore as well.
 

SecondAmend

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Weaker ammo will run faster as it does not push the bolt through the entire stroke length. Even weaker ammo short strokes to the point of not catching the sear and running away. Which particular ammo generates the lowest ROF while maintaining proper operation will depend on the recoil spring strength.

MHO, YMMV, etc.
 

Slowmo

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Probably depends a lot on the condition of your recoil spring. I doubt there is a universal answer. You mentioned your barrel is threaded, so if you’re using a suppressor, that’ll also affect the answer.
 

slimshady

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Single load the magazine and semi auto, once you have a load that consistently catches the bolt you use a full magazine with a dummy round for second shot to account for the drag. Probably take a few tenths to compensate, that is your minimum safe load.

Be aware dirt, temp, dryness vs lubed, etc. may increase drag enough to cause a runaway. UZIs like full power ammo, not light.
 

AKarms

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You can always cut coils off the spring to try and balance it out. But again use caution
 

gundisaster

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Not sure why you’d do that. Just make standard 147 grain subsonic ammo. Runs great and sounds great suppressed. 158 grain bullets sound even better. Go heavier not lighter.
 

amphibian

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Not sure why you’d do that. Just make standard 147 grain subsonic ammo. Runs great and sounds great suppressed. 158 grain bullets sound even better. Go heavier not lighter.
Some people like to go cheap and / or tinker.
I've been loading almost exclusively 147Gr 9mm subsonic for 20+ years. I load relatively hot and want the same ammo to run all my 9mm guns. All that said, I've dabbled in doing subsonics in 155, 158 etc as well as some 124Gr subsonic. A recent thread on here about doing 115 Gr subsonic which I have never tried. So I got some to mess with....definitely not replacing my goto 147Gr loadings but it may be an option if things get tight with 147Gr projectile availability / price.
 

SecondAmend

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FWIW, on Sep. 8, 2021 I tested the 9mm ROF in my full size Uzi with the same magazine, bolt, and recoil spring. Rounds Per Minute ROFs were as follows:
Blazer Brass, 115 gr., RN: 578;
Federal AE, 115 gr, RN.: 579; and
Federal 147 gr., FP: 613.

MHO, YMMV, etc.
 
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Dirk Hawthorne

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Not sure why you’d do that. Just make standard 147 grain subsonic ammo. Runs great and sounds great suppressed. 158 grain bullets sound even better. Go heavier not lighter.

I'm just tinkering around.

I figured one of you guys here on uzitalk would have tried it already. Doubtlessly someone has.
 

amphibian

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I'm just tinkering around.

I figured one of you guys here on uzitalk would have tried it already. Doubtlessly someone has.
User K2 on here has done this extensively. He also slugs his bores and likes to use larger diameter .357 or so (can't remember) bullets that generate higher pressures and also use a light powder charge. I can't remember all the details. Maybe he will post on here.
 

Dirk Hawthorne

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I tested some subsonic 124 grain LRN ammo in my Vector.

I decided on 1050fps as the velocity. This is the speed of sound at 30 degrees F, minus about 35 fps to account for variation in bullet velocity. I don't shoot when it's colder than 30 F unless I'm really desperate to go shooting.

The ammo was super accurate. The threaded 8.5 KAK barrel I use with my Bowers suppressor is noticeably more accurate than my other barrels.

The recoil was really low and the suppression was really good, it was very quiet.

The gun worked fine until it got just a little dirty and then I had a ton of FTF and stovepipes, a couple of doubles on semi. So basically the gun ran like crap.

If someone was dead set on getting this to work, I'm sure it could be done if you clipped some coils off the recoil spring, or you pushed the velocity up higher, but I'm not bother with it again. The juice isn't worth the squeeze.

Just in case anyone was interested, I used the lowest load listed for Winchester WSF with a 125 grain bullet in the Lyman 48th edition reloading manual. The manual lists it at 950fps, but that's for a handgun. The extra length of the FBI barrel made it chronograph at 1050.
 

CKxx

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I've done something similar. I wanted to develop a 147gr 9mm load that would be "easy" on the gun for longevity. DON'T HANG YOUR HAT ON THIS, but I ended up with 3.2gr of vvN320 behind an Xtreme or Berrys 147gr round nose. While developing it, I recorded the gun firing in slow motion and kept reducing the charge until the bolt was just barely kissing the rear of the receiver/buffer. You could empoly the same slow-mo cellhphone tecnique to be sure your bolt is getting to the rear of the gun and thus safely traveling well beyond the range requred to catch the sear.

The same method worked for my UZI, STEN, and a Lage upper.
 

Dirk Hawthorne

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Why are you worried about longevity? Are there any instances of an UZI getting damaged by firing full "standard" velocity ammo?
My general impression is that the UZI is a very robust gun.

What I did here with this experiment is:

1. Pick a velocity (1,050) that would provide a reasonable buffer to stay below the speed of sound, even in very cold air.

2. Load 124 grain ammo to that velocity.

The gun ran like crap at this low velocity with 124 grain bullets, so unless I can come up with a rational reason to increase the velocity higher than 1,050 fps, the experiment was a flop.

I'm not sorry I did it, because now I know what the lower limit is for my gun in terms of the momentum of the bullet and powder.

124 grains x 1,050 fps + 3.4 grains of powder x 4,200 fps = 145,000 gr ft/sec.. I know that the lowest number that will sort of run in my perfectly clean UZI.

The same number for Federal Am Eagle 124 gr FMJ is like 169,000, which runs the gun even if it has 400+ rounds through it already.
 
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