Sunday, August 4, 2013

Modifying the Uzi bolt to semi auto

Continuing one with our Uzi project......
The SMG bolt must be modified in such a way that it can no longer be used as a fully automatic bolt, and can only be used to fire semi automatically. One shot per pull of the trigger, and all that.
This is probably the hardest part of building an Uzi, and requires the use of a milling machine. A drill press and a cutoff wheel could be used, but would also require abundant use of a file to get everything spot on.
Semiautomatic bolts can be purchased, however, in lieu of machining your own. I'm a real tightwad when it comes to stuff like that, and I own a number of machine tools, so I just forgo spending the money on the finished parts, and instead spend my money on screwing up one or two parts before finally lucking out and getting one right, in effect wasting twice the time and money that could have been spent on simply purchasing an off-the-shelf part.

Starting with pics from a previous post, we took our annealed bolts and drilled a hole in the rear of the bolt, all the way through to where the fixed firing pin was. This allows for a floating firing pin to be used.
We also drilled a 1/4" hole in the upper right corner of the bolt. This is to save us a little time on the mill, down the road.





Next, the sear "feet" on the front of the bolt are welded up. This is so the original sear will no longer control movement of the bolt. I laid a ton of weld on these areas, just so I knew that I wouldn't have to go back and add more after machining the welds down flat with surrounding areas. Hence the "gob-welded" look.
On the left, an un-modified bolt, in the middle, a welded bolt, and lastly, a bolt with the welds milled and sanded smooth.


Next, we will be revisiting that hole drilled in the upper right corner of the bolt. This hole is there so we can mill out a slot on the right side of the bolt and the bolt can now clear the blocking bar in the receiver. I milled this out with a 1/4" end mill, then started filing to get it to clear the bar by a few thou.


Here is more of the bolt with appropriate areas filed and sanded flat.


Now, we need to machine a large chunk out of the bottom right side of the bolt, so the semi auto sear has a place to ride. I thought I got a pic of this entire process, but it seems I only got a half-way-through pic.


After a couple of failed attempts to machine the striker (mainly because my milling machine is in pieces at the moment, getting some upgrades), I ordered a striker for the gun.

Since I'm building a carbine, the gun must have a 16" barrel, and have an overall length of 26" with the stock collapsed. In order to facilitate that, I had to make sure my barrel was long enough. I turned my barrel out of a 11" barrel blank, and machined a barrel extension 7.5" long that I welded on to the 11" barrel to make it a permanently-legal carbine barrel. Since I think the Uzi carbines look ridiculous with the "ant-eater snout" barrels, I used a piece of 6061 aluminum tube to make a fake suppressor, so the Uzi wouldn't look quite so dorky.
Here is the finished, raw metal Uzi, with the fake can on it. I intend to do a little machine work on the can to make it resemble a real suppressor, more than it does now.

I'll have pics up in a few weeks of the finished product, and hopefully a range report.

For the purposes of 922r, I have the following parts to replace the original imports.

Receiver -US
Barrel - US
Mounting Blocks (trunnions) - IMPORT
Bolt - IMPORT
Trigger housing -  IMPORT
Trigger - IMPORT
Sear - IMPORT
Disconnector - IMPORT
Buttstock - IMPORT
Forearm/handguard - US
Magazine body - IMPORT
Floorplate - IMPORT
Follower - IMPORT

That brings me to 10 import parts, which means I am legal and ready to go. I'm waiting on the striker and forearm/handguards to arrive.
There was once a letter from the BATFE that the Uzi had an operating rod that was subject to 922r, but they have since changed their opinion and said that the Uzi did not have an op rod, which is altogether correct.

More on this project as I get to it.........

7 comments:

  1. Is the fake can going to be permanently attached to reach the 16" length so you can keep the shoulder stock?

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    Replies
    1. The fake can simply covers the 7.5" barrel extension I welded on. The barrel is now 18.5 inches long.

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  2. Awesome James,
    I think the aluminum tube needs a good rattle can flat black paint job though.
    The things you can do in the garage just blow me away, figuratively speaking.;)

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    1. The Uzi is actually fully stripped of paint in the picture and is awaiting a fresh coat of Uzi green Duracoat. The fake suppressor is getting a little machine work and finish work before being sprayed with flat black duracoat.

      It's far from done, but I always enjoy putting up progress photos and teaser shots.

      Thank you for your compliments.

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  3. great job buddy , did you do the annealing on the bolt yourself or send it out to someone ? are you planning on also enlarging the ejection area of the bolt like the commercial ones, or will it be good to go as is ? and lastly are you doing a build thread on any of the build forums(weaponguild,homegunsmith,ect) would love to follow a bit closer

    thanks for the blog :)

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    Replies
    1. Thanks for the kind words!

      I have a friend on the Guild who anneals them for me, but the only reason I don't anneal them is because I don't have a barbecue grill. =)

      I don't plan to enlarge the ejection area unless repeated tests show it to be necessary.

      I will be doing a build thread on the Guild, but wanted to wait until it was painted and test fired.
      If you liked the blog entry with pics, you'll love what I am working on now, video. =)

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  4. I appreciate everything you have added to my knowledge base.Admiring the time and effort you put into your blog and detailed information you offer.Thanks.
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    ReplyDelete