Thursday, August 1, 2013

Converting the Uzi fire control group to semi auto.

Back on the Uzi carbine I'm building........

I ended the last installment of this project with two receiver sections that had been welded together out of four sections. Before I could go much further, I had to weld a blocking bar in place on the receiver, which is shown in the pictures below.
Once the blocking bar was in place and burned in, I took another receiver section from a demilled Uzi receiver I got from Apex gun parts. The receivers they sell aren't good for much, but they do have the necessary center section with the ejection port.
Here is the receiver in one piece. There is still a little grinding and sanding left to do on the welded areas, but for now, it's legally a firearm.


There was a small amount of burn through on the welds that hold the blocking bar in place, these were ground out with a Dremel tool.



Another shot of the quasi-finished receiver.



Now, as with any semi-auto that is built from what was originally a machinegun, you have to modify everything that once enabled the weapon to fire in fully automatic mode. The blocking bar welded in previously keeps a unmodified bolt from being inserted in the weapon, and I have to heavily modify the bolt for it to function in semi auto only.
The next item on the list is the lower, or grip area. A block is welded in place to keep the selector switch from going into the full auto notch. This is just a piece of 1/8" thick scrap metal I burned in and ground down. Nothing special, but it works.
 Here you can see that the selector is in semi auto mode, and is unable to be pushed forward into full auto.

 The selector in semi. You can see that the L shaped link cannot go any farther forward as it is blocked by the welded in metal.

Next, I put the trigger group back in.
Before I put the group back in, I ground the right hand side sear off, so it would no longer control the bolt movement. When I modified the bolts to semi (More on that in another post), I welded up the old sear trip areas, so even IF an unmodified lower were put in the gun (which it can't, more on that in a second), it would be useless as there are no sear surfaces left on the bolt.
 If you look closely, you can see the sear tab on the right side is missing altogether. The left sear tab remains, as that is how the striker will be controlled.

After these modifications were complete, I narrowed the notch at the front of the lower, and welded up the slot in the receiver to match. This way, the slot that the lower's front tab rests in cannot accept a full auto, unmodified lower. It can only accept my highly modified lower.
To top this off, I will also weld up the hole in the receiver where the right side sear hole is. This should show anyone who is paying attention that I have no intentions of ever converting this gun to fire fully automatic.

Next up is the bolt modifications and striker, but that will be the topic of another post.

I hope this, and all of my other building posts, are educational and fun, and inspire some of you out there to build your own legal Uzi carbine or pistol.

9 comments:

  1. I just wish I was up there handing you tools so I could learn this stuff myself. Give me an old smoke pole and I can rework it into a pretty good looking and shooting rifle. The more modern stuff, I'm just a part replacer and part finisher.

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    1. There's really not a whole lot to learn about rebuilding old parts kits. The learning curve really isn't very steep at all. I guess the toughest thing would be learning how to weld and/or use a lathe and mill, but even that isn't very hard.

      You are, however, welcome to come work on (or build) a gun any time you like.

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    2. Thankee Sir, until we got the lathe in the shop we did either the drill mounted in the vise or the drill press as our lathe. For small stuff such as firing pins and even coil springs I still use the drill in the vise trick. With a router speed control with a multi-speed drill I could get the chuck down to 15 RPM or as high as 950 RPM on the 3/8th's on the 1/2 inch I could only get it down to 50 RPM but up to 1100 RPM on high. My largest issue with the lathe we had was I had just never really worked with one until then so I was a bit scared of it.

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    3. I use a lathe all the time, and still have a healthy amount of fear and respect for it. I've rapped my knuckles too many times on the chuck and even had a few stitches as a result of not paying attention to the lathe.

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    4. 'Tis right to be scared of machinery that can remove appendages :)

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  2. Im curious about your selector block, is there some legal reason why you couldn't have an (obviously) non functional selector that still swings from semi to full? Just cause Im the type of geek that would do such a thing before muttering lines from First blood or or something. Fell in lust with an MP5 kit on GB the other day with the embossed selector graphics on the lower, bullet with x for safe single bullet for semi 3 for burst and like 10 for full! Definitely out of my budget for now but.....

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    1. MP5 kits are waaaaay overpriced. I'm working on one now that is a mishmash of surplus German parts and home-made stuff, should come out under 350 for the whole thing.

      I can't see any problem with it, but I'm not the ATF. I have seen a number of other firearms that have original FA lowers but the ability to work in FA was permanently removed. The selector would move to that position, but it did nothing.
      Pretty much any/every HK lower on the market will work this way when all semiauto parts are used in it; semi is still semiauto and FA is semiauto as well.

      Problem with the Uzi lower is that it would be marginally difficult to make it work as you're suggesting. The FCG is very simple, but complex as well. Trying to make it work any other way might result in total failure.

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  3. I talked to an ATF agent today and he was great to talk to with all my questions. I asked about building a uzi parts kit he informed me that even if i put the block in like your above it would still be considered a machine gun because it has an open bolt with a fixed firing pin to be truly semi it would need to have a firing pin and a hammer on the SBR he said that a fake suppressor would work as long as it was attached permanently. He was great to talk to and did not make me feel like i was being drilled for even considering putting one back together I will defiantly call the again with any questions.

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    1. Sigh.
      At no point did I EVER say that it was okay to keep a fixed firing pin on your bolt. IF YOU HAD BOTHERED TO LOOK AT ANYTHING ELSE, YOU WOULD HAVE NOTICED THAT I'VE MENTIONED CONVERTING THE BOLT TO SEMI AUTO. IT DOES NOT INVOLVE A HAMMER AT ALL, IT USES A STRIKER.
      Your comment is suggesting that I have effectively advised that no mods to the bolt are needed, and that is 100% unmitigated total horseshit. ANYTHING THAT FUNCTIONS IN THE OPEN BOLT CONFIG IS A MACHINEGUN. PERIOD, FULL STOP.
      IF YOU ARE EVEN REMOTELY CONSIDERING BUILDING YOUR OWN GUN, DO YOUR HOMEWORK AND RESEARCH BEFORE EVER EVEN THINKING OF TALKING TO THE BATFE, OR POSTING BULLSHIT NONSENSE ON THIS BLOG.

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