Well, the board is either fixed, or it's going to run terribly. Cross your fingers and hope for the best. I'm at my technical limit right now.

Sten Mk III

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jbs
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Sten Mk III

#1 Post by jbs » Sun Jul 02, 2017 9:18 am

This is my crude version of a Stem Mk III kit build. There are kits from a few vendors that you can get that give you a resized bolt and tube but I chose to keep the original size tube and bolt. To do this, you must use some type of denial pin so a full auto bolt cannot fit.
I also wanted to use the original trigger setup but wanted to use a more reliable trigger group. I ended up using an AR trigger group. I also used an AR firing pin that I got from a vendor on weapons guild. The pin comes in a sleeve so rather than drill different diameters to specific distances I was able to drill one size hole, press in the sleeve and pin it in place.
SInce the sten is a blowback system, any weight taken from the bolt needs to be put back. You'll see in the pics how weight is added back to the bolt by making a new seat for the buffer spring.
I didn't want to build a pistol so the barrel needed to be more than 16". I don't like the anteater look so the tube goes almost to the end of the barrel. The look is awesome but weight is increased. It's pretty heavy.

Read as much as you can about builds people have done before attempting. If using a tube and bolt kit from one of the vendors you find on the web it is pretty much straight forward. It took me about 2 months to do it the way I did with some trial and error and allot of info from other kit builds. I have a mini lathe, a mini mill and a mig so some things were much easier to do but could still be done without the mill and lathe (dremel or drill press) but you'll need some type of welder.

Here's the kit as I got it.
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jbs
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Re: Sten Mk III

#2 Post by jbs » Sun Jul 02, 2017 9:19 am

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All this had to be de-milled or cleaned up so the parts could be used.


I found and printed a template for the tube. I got the 9mm pistol barrel from a vendorand added an extension tube to it to meet required length. CThe barrel was welded to the front trunnion than the tube was welded to the trunnion to create the extension.
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The template is wrapped around the new tube so cuts can be made. On this template, the brass deflector rivet holes were backwards so check with your parts before cutting and drilling.
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Last edited by jbs on Sun Jul 02, 2017 9:27 am, edited 1 time in total.

dogboysdad
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Re: Sten Mk III

#3 Post by dogboysdad » Sun Jul 02, 2017 9:21 am

I have a kit somewhere. I can't wait to see how this turns out.

B32dominator
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Re: Sten Mk III

#4 Post by B32dominator » Sun Jul 02, 2017 9:34 am

I've always wanted to build one but I have no idea how to weld or own the equipment.

jbs
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Re: Sten Mk III

#5 Post by jbs » Sun Jul 02, 2017 9:36 am

Trigger group is all cleaned up. The barrel is welded to the trunnion and extension. Welds coulda been better but it won't be seen. I used a freeze plug of the appropriate size as a new front trunnion to go at the end of the tube. The assemblt is slid into place in the tube and drilled and riveted into place.
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So that a full auto bolt can't be used, I installed a denial pin. This is 1/8" round bar welded to the trunnion and tube. As you can see, the bolt cannot get to the chamber past the pin.
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jbs
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Re: Sten Mk III

#6 Post by jbs » Sun Jul 02, 2017 9:50 am

Continued on adding the deflector, riveting trunnions and I drilled decorative cooling holes in the tube. Looks good and also shaves some weight off of the gun. You can see the amount of barrel I decided to extend past the end of the tube.
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Time to move on to the mag and mag well.
The mag parts

The mag well when cleaned up should keep as much metal extending from it. It needs to be welded to the new tube so you need those pieces or flaps when you cut it off the old tube. The mag well also has the ejector. It all needs to be in the right place to function properly. You can place the magwell in place with the bolt installed up to the denial pin to set the ejector height. Tack it in place and than put in a mag with a round or snap cap and make sure it will feed when the bolt contacts it. It should start pushing the round before hitting the denial pin. If it looks good, weld in the magwell.
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Re: Sten Mk III

#7 Post by jbs » Sun Jul 02, 2017 9:52 am

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Since I stretched the tube out to the end of the barrel, I wanted to stretch the trigger guard. I also wanted to use the original trigger group but wanted a more reliable trigger. The way I did this was to place an AR trigger group in the guard extension and linkage it to the original trigger.
I had to fab a box for the AR trigger to fit into the guard extension.
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Re: Sten Mk III

#8 Post by jbs » Sun Jul 02, 2017 10:03 am

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jbs
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Re: Sten Mk III

#9 Post by jbs » Sun Jul 02, 2017 10:14 am

Now I had to mod the bolt. It was drilled for the AR firing pin sleeve and the sleeve inserted and pinned. A groove had to be cut to allow the bolt to ride over the denial pin.
Since the hammer path would go through the area where the buffer spring rides, a new seat had to be made. I used a short length of tubing or conduit cut to fit the tail of the bolt and a larger tube to fit the short length and act as a seat for the buffer spring. These were welded in place.
The hammer travel path was determined and this area was milled out to allow it to hit the firing pin and reset.
Also, the bolt handle going through the bolt hit the hammer path so a new bolt handle had to be fabbed.
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Last edited by jbs on Sun Jul 02, 2017 8:30 pm, edited 1 time in total.

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Re: Sten Mk III

#10 Post by jbs » Sun Jul 02, 2017 10:24 am

The trigger group needed to be connected to the original trigger. I did this with a linkage between the two. When you need to do machine work to an AR trigger, it is extremely hard. It will need to be softened before you should attempt to cut or drill. Heating with a torch will do this for you. Do a search to find the exact directions.
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At this point it can be tested for mag feed, cycle, action, and safety. Everything worked as it should. Loads from teh mag, fires, ejects, reloads, safety functions.

Still left is to fab a cover for the trigger guard, attach the front sight, smooth down the welds some and give it a coat of paint.

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Re: Sten Mk III

#11 Post by jbs » Sun Jul 02, 2017 10:28 am

I think I got everything in the build. It's been a few years since I did this kit.
Here's my version of a stretched sten.
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Re: Sten Mk III

#12 Post by Phantomrig » Sun Jul 02, 2017 8:20 pm

Great looking build, thank you for posting this. It gives me a bunch to go off for my build should it happen.
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