My loosening mini Uzi barrel nut causing FTfire. See vids.

[rhouston8]

So my registered bolt , open bolt Mini is acting up whereas it used to run fine. I get light primer strikes and failure to fire. This happens in semi as well as FA shooting. What happens is I start with a tight nut and a barrel that doesn't move at all. I shoot several rounds in even semi. This causes the barrel to loosen and have slop including a tiny amount of back-fwd slop. This causes light primer strikes. I tighten the piss out of the nut and it loosens ever so slightly again and the crap happens again. Interestingly this same small slip in the barrel/nut loosening occurs with my full size RR but doesn't cause an issue at all.

The teeth on the barrel nuts look OK and uniform to me. In fact swapping the nuts from full size to mini doesn't help matters. Likewise the barrel nut holder ( whatever it's called) looks ok and the same as my full size to my untrained eye. I do suspect that I must either change it or change the barrel itself. Bottom line is that my barrel is moving fwd ever so slightly and this prevents the firing pin from solidly contacting the primer. The firing pin itself looks fine to me by the way.

All advice much appreciated. I REALLY hate mailing off MGs for repair. The whole registered mail thing and whatnot is a huge pain in the ass as yall know.

See vids here.
Thanks

https://picasaweb.google.com/rhouston8/MiniUziBarrelNut?authkey=Gv1sRgCN-plMfIut_i3QE

 

[dubagel]

You may just need a new spring on the barrel retaining nut pin/plunger. It may not be providing enough tension on the plunger with the inertia when the bolt is cycling. You may also want to look at the rubber buffer in the back of the receiver.

 

[BWE Firearms]

Check your barrel nut teeth and the edge on the barrel nut catch to make sure thee are not worn. If they are fine replace the barrel nut catch spring.

 

[rhouston8]

^^ the teeth and catch surface all look crisp with sharp angles.

I think replacing that catch spring is the key...esp if yall feel that's reasonable. The gun is fairly violent and I ran it with a thick buffer previously which made it like a crazy 1400 rpm. Way faster than any Subgun I own or have shot. Unnaturally fast. But ran it did. Until the recoil spring crapped out along with the blackjack buffer which compressed into a rock hard block which deep engraving in it from all the pounding. Interestingly once I removed the crapped out recoil assembly & buffer and replaced it with a simple mil surplus factory mini recoil spring assembly the gun still ran fine but two things happened. Related or not. One- the new slower ROF ( still fast but more like a mini should run. I'd guess 900 rpm) causes much more uncomfortable vibrations at the cheek weld. I mean it will bruise your dang face. No fun. I started shooting the gun from my hip. And I'm not a sensitive guy by any means. This suckers wire stock was a dental drill bit on your face. Even in semi. Whereas with the fat buffer the rpm increased enough to cause the vibrations to level out at more of a hum. Not nearly as painful.

TWO- after I swapped out the screwed up recoil assembly and removed the buffer ...that's about when I noticed the barrel loosening starting to occur and cause failure to fires/light primer strikes.

Ok. Anything special I need to know about replacing that catch spring??? I hope RTG had them in stock. I simply haven't ever had to replace anything on any of my Uzis therefore I don't know much technical/repair crud concerning them ( unlike the HKs).

 

[RoverDave]

The uncomfortable vibrations in your cheek weld could be due to the bolt hitting the back of the receiver. In a factory open bolt full auto Mini UZI, there's a 3/8" thick black buffer in the back of the receiver. The buffer has a hole in it so the guide rod/spring goes all the way back to the receiver. The guide rod/spring is shorter than the one for the full size UZI and it does not have a red pad on it. If you are shooting your gun without a black buffer, the bolt may be hitting the back of the receiver and it's very jarring. Many years ago when some of us were playing around with spring and buffer variations, I found the same thing - if you let the bolt hit the back of the receiver it's so jarring you don't want to shoot the gun.

Maybe that is also having some effect on your barrel nut loosening.

 

[rhouston8]

^^excellent info for me. Thanks. No, I did not realize that the minis normally ran w a thick black buffer back in there. I just assumed the proper setup was like a full size with the thin red cardboard like pad at the tail end of the recoil rod.

Makes complete sense. Man the vibrations were awful w/o that buffer in there. And yep. I bet that did contribute greatly to the loosening barrel as the whole thing was quite violent.

Good to know. Buffer goes back in and I'll re assess and prob replace that catch spring.

 

[RoverDave]

Keep in mind that on the originals, the guide rod/spring goes through the buffer all the way to the back of the receiver. If you previously had a buffer and then a recoil spring stacked on top of that, that might account for your higher rate of fire.

 

[cajun 22]

I doubt that my problem is the same but here is some info just in case someone has a similar issue. I had the same problem with a semi-auto, sbr, mini uzi. There was no problem shooting unsupressed with any barrel. When I used the barrel nut adapter for the Gemtech MK9K the can would start to shoot loose after a mag. I solved the problem by taking a little material off of the inside of the back portion of the barrel nut catch. This allowed the catch to come foward just a little bit to engage the teeth on the nut. Problem solved.

Good Luck

 

[TexPaul]

After reading this thread, I've been trying to locate a spare buffer for my open bolt Mini. I'm having no luck at all. Does anyone know a source for Mini parts? Thanks.

 

[RoverDave]

The Mini buffers are the same height and width as a buffer for the full size UZI, so just get any UZI buffer you can find and cut to to the thickness you want. Some people cut down the buffer used in the semi-auto UZI. Blackjack sells a variety of sizes here.