Mk2 Sten Build Questions

ianian · Sep 21, 2023

Hey y'all, I'm in the process of building a MK2 Sten and I had a couple of questions:

1. Is a smaller diameter semi auto tube required? I didn't know these were a thing and milled out a regular diameter tube- hoping it will still work

2. How is the front barrel trunnion transferred from the donor kit to the new receiver tube?

3. With the lower trigger pack detached, should the hammer fly forward when the trigger is pulled and lock back when reset manually, similar to an AR? Mine doesn't.

4. I'm hoping to go with a mock silencer look. Should I get a standard barrel and weld an extension or splurge for a 16" barrel?

Thanks so much in advance!

Deerhurst · Sep 21, 2023

As far as I know the Sten has no hammer and is open bolt.

I have done a few build but not yet a sten. Picks would be welcome to see what you are working with.

root · Sep 22, 2023

You will need a denial bar like a UZI on a standard size tube and bolt.
You will also need to mod the bolt to accept a floating firing pin and use some type of semi FCG that does NOT allow hammer/ striker follow.
it must also fire from a closed bolt
You can build a pistol with a sten grip or build a carbine with a stock & 16 inch barrel.

Machines are best for the build but many stens have been built legally semi with files, dremmel, & flux cored wire.

A lot of buildz use the AR15 fcg with a transfer bar for the build but there are @ a million ways fo make it legal & semi.
It's a custom build it only has to work with your gun not be compatible with every last semi sten out there.

ericthered · Sep 22, 2023

The sten is a open bolt that you are converting to a closed bolt striker fired. Basically the same as a Uzi. I dont know to much about stens, but would think the select fire mechanism would be a similar design to the uzi in as far as how the sear behaves. If you remove a Uzi grip in semi auto and squeeze the trigger, your sear will pop up like a hammer. If you look close the sear will drop first before popping up. The drop is releasing the striker (or bolt on open bolts) then the popping back up is normally stopped by the upper receiver so the sear is reset to catch the striker. So basically you are seeing normal operation.

As far as barrel length goes, if you went full 16" then you can trim it down in the future if you wanted to SBR it or permanently attach a suppressor. Plus while in 16" configuration you will have a higher velocity then a stubby barrel.

Here are part one and two of some dudes sten build. He recommended buying a new bolt. He noted that semi receivers are smaller then auto receivers. Which may be in instead of a blocking bar? Which if your converting a fa bolt to semi then you would probably have to have it turned down as well as drilled for the firing pin (the fixed firing pin on bolts are heat treated to be quite hard).

The Do-It-Yourself Sten: Part One

Sten Nation Of all the semiautomatic firearms that one can build, the STEN has to be the easiest to and requires the least amount of investment in both tools and time to complete....

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