Need help got semi going full occaisionally

[Lethal Farce]

Picked up a Model B that looked to be in mint condition. First time shooting today I was getting a good many light primer strikes w/o ignition. But the kicker was several two & three round bursts when trying to shoot fast. Is this fixable or should I take it back to the guy I got it from? What would cause this? Any help would be greatly appreciated.
LF

 

[davidl]

sounds like weak ammo to me, as in your bolt is not traveling back far enough. try hotter rounds.

 

[RoverDave]

LF, welcome to UZI Talk. Congrats on the new UZI. Don't give up on it yet!

For the gun to shoot bursts, the bolt has to come back far enough to eject the empty and strip off a new round from the mag but not far enough for the carrier to catch on the sear and thus stop it from firing a second round. There can be a number of causes. As davidl mentioned, weak ammo is a common cause. Try it again with hot ammo. Remember that off the shelf 9mm ammo is generally loaded for pistols and can be quite weak in an UZI.

If that doesn't fix it, then look for something that is causing friction so the bolt doesn't move freely. If the bolt is hindered in some way you'll see the results you mentioned. Things that could cause friction:

- A very dirty gun. Disassemble and look at the bolt and inside of receiver for excessive crud. Clean if necessary.
- Magazine might be rubbing against the bottom of the bolt. If it does it will slow the bolt down. Try a different magazine if you have access to one.
- Bolt might be rubbing on the receiver or top cover in some strange way. To test, remove the magazine and the entire lower (by pulling out the one push pin that holds it in place. Take the bolt out of the gun and remove the recoil springs. Put the bolt back in the gun and title the gun forward and backward. The bolt should slide freely. Put the top cover back on and do the same thing. You should be able to hear it slide freely.

If it's not one of these, the problem could be slightly more serious. It may be that the bolt is coming back far enough but the sear is not holding back the carrier. Again that could have several causes:

- Could be wear of manufacturing problem with the front edge of the carrier.
- Could be wear of manufacturing problem with the sear.
- Could be that the lower is not positioned correctly. This has happened before. If the front end of the grip assemble hangs too low away from the receiver, the sear might not be high enough to catch striker.

Give these things a try and let us know the results.

 

[Funker]

Check your lower

If all of the above does not work take off your lower and make sure that your trigger spring is installed correctly .Once on my Semi"A" I had half of the trigger spring come off and it did not apply enough pressure on the sear for it to trip back into position ,it would hold the sear down and it caused double shots then stove pipe

 

[Lethal Farce]

Thanks, everybody. Your help is greatly appreciated. I work my way thru the ideas. BTW it was CCI Blazer ammo I was using.
LF

 

[mlee36]

I interpret your situation a little differently than the other guys here. If it is indeed a semi-auto Model B it fires from a closed bolt. Therefore, it has a firing pin which may be malfunctioning. Take the bolt out of the gun and remove the firing pin and clean out any crud. Lightly oil it and make sure the firing pin spring is operating correctly.

In a closed bolt the sear only releases the firing pin. It sounds like it may be sticking in order to fire full auto or no fire at all.

 

[RoverDave]

I think it's a good suggestion to check everything for crud, but I'm not convinced that a sticky firing pin would cause these results. If the firing pin was stuck forward you should experience FTF because the semi bolt face doesn't have a lower lip. Because of that the rim of the case would hit the side of the firing pin and jam. That's the reason the ATF insisted the the lower rim on the bolt face be removed on the semi autos.

 

[Lethal Farce]

Thanks again. I called the guy I got it from. Seemed a little defensive at first. He said he hadn't shot it since he bought it in the 80's. Claimed "Shot a couple of mags, than put it away". Hadn't been touched since. I'll open it up tonite and let y'all know
LF

 

[RoverDave]

Here's another thought. If it has been stored for a long time, the fire control parts could be gummed up, causing the sear to sometimes get stuck in the down position. I'd say the chances are very good that if you cleaned the gun thoroughly and used hot ammo, the gun would function properly.

 

[Lethal Farce]

Amazing is a good word for the Uzi. I had it completely apart and lower removed w/o any tools in minutes, and thats with never having worked on an Uzi before. It was a little gunky where the bolt rides, and in the extractor area. By reputation of these being so reliable, I can't imagine mine was dirty enough to cause problems. Its lubed up and ready to go. When y'all say hotter ammo, what do you recommend. Is the white box Winchester good enough? I planned on shooting the cheap stuff in this.
LF

 

[RoverDave]

You don't know a gun until you take her apart. Very nice design, isn't it?

A lot of guys shoot the Winchester White box and it should work fine for you. It can sometimes be a little inconsistent but it's fine for your function test. Let us know how it goes. Bring a spare mag along if you have one. Ammo and mags are the easiest thing to switch if you're have any trouble.

 

[Lethal Farce]

Sorry, it took so long. Got the Uzi back to the outdoor range w/ a high back stop. Good thing!! It was worse now that I cleaned and oiled. I also tried some 9mm NATO that I got from Ga. Arms, it should have been a good bit hotter than the Blazer. Talk about a wake up, pull the trigger and dump half a magazine. Any other things to try? Is it possible to buy some of the parts that may have worn down?

 

[bruce]

You can buy any SA parts you need from D and D Sales (520) 883-3846. Talk to Dan.

Before buying anything, maybe a creative former owner installed a full auto sear. If so, the lobes are larger and it may sticking on the receiver frame. The holes on a FA are larger.

 

[Lethal Farce]

Thanks, Bruce.
I appreciate the help. I wish I had mentioned this before, but didn't really understand or think it was important what the previous owner had told me. He had said he had put a registered full auto bolt in it the time he shot it, and claimed that the original bolt w/ a replacement legal barrel was installed right before he sold it to me. I did not realize that there were different sears. Do you I should buy a sear before trying anything else?
LF

 

[RoverDave]

There's no guarantee that he put a FA sear in the gun when he had the registered bolt in it, but it's a possibility and could account for the behavior you're seeing. If you could find someone in your area with a semi UZI, the easiest thing to do is take the entire lower pistol grip assembly from their gun and pop it on to your gun (just need to pull the one large pin that holds on the lower assembly.) You don't have a surplus full auto lower on your gun, do you?

Oh and you might not want to use full mags when you do more testing...

 

[Lethal Farce]

Thanks, RoverDave. Good advise on the mag. No I don't know of any other Uzis around here. I am pretty sure it is the correct lower, ie no auto position on the safety switch. A new sear is probably the quickest and cheapest next step. What should the surface of the sear look like?
LF

 

[RoverDave]

Here's a photo that Amphibian took comparing the different sears.

The semi sear for a full size UZI is A, the full auto sear for most full size UZIs is C. The critical thing is the width of the two pads the stick up through the receiver. (The two vertical protrusions on the lower part of the sear in this photo.) Notice that the pads on the semi sear are not as wide as on the full auto, thus they fit better in the smaller hole on the semi receiver.

Another way to check it is to remove your top cover and bolt from your gun. When you pull the trigger, you'll see two little feet pop up through two holes in the bottom of the receiver. There should be plenty of clearence for the feet in those holes. If it's close, you probably have a full auto sear in the gun.

 

[bruce]

Filing

If your sear is sticking, the easiest solution is to file out the holes a little at a time until the lobes clear easily, like the previous post suggests. A small triangular file is best.

SA sears are offered on bulletin boards and auctions regularly. There is a posting in the reference section of Uzitalk on reassembly of lowers, if you forget something.

 

[Lethal Farce]

You guys are great, thanks for all the help. I called Dan @D&D, he was a big help. He suggested lookig at the top cover to see if bowed up in middle and also said to examine sear. I'll order the spare parts from him today. RoverDave, my sear is different than all shown. the top surface of my lobes looks longer front to rear than the SA shown, also the leading edge side appears to have been shaped w/ a file. When you said wide were you referring to side to side or front to rear?
LF

 

[RoverDave]

When I said wide, I was refering to front to rear, not side to side. Sounds like you may have a full auto sear that someone tried to modify to run in the semi receiver. Best bet is to get a semi sear. I wouldn't enlarge the holes in the receiver. Modifying the receiver to accept full auto parts is a gray area. ATF allows certain modifications and not others so it's best to stay clear of that.