Building the Canadian Semi-Auto STEN

[Claven2]

Mick, the trick with the MIG is to use it at very high power. I have a dedicated 20A circuit for my machine and upgraded wiring to handle the extra impedance. To get good mag box welds, I crank up the power - literally.

[tiriaq]

The originals were welded using electric arc, oxygen/acetylene gas or electric resistance (spot) welding. Soft solder and rivets, too, on some, depending on the Mark, and/or period of manufacture. The ladies who assembled the originals would have been amazed to see a MIG, TIG, or flux cored wire feed welder in operation.

[Mick]

I have done some experimenting with my mig, and no matter what I can not do anything like what you can do with your mig. What you have done looks just like tig welding to me, I'm amazed.

[tiriaq]

Generally speaking, assuming that the machine is set for the appropriate amperage, and wire speed, and gas flow are correct, it is a matter of practice, and more practice. I remember when I first used a MIG, there were bits of wire stuck all over the place. One of my future purchases is going to be an auto darkening helmet. Just one less thing to have to mess with at the critical moment.
I have carefully examined a pair of rifle actions made from a couple of Mausers - one short, one long. The receivers, bolts, firing pins and magazine boxes had been cut and TIG welded. It was not apparent that any welding had been done. I am sure that Claven2 has seen these. Remarkable what a first class TIG welder can do.

[Claven2]

Yes, I've seen the mausers in question I kind of know the smith who built them rather well...

As for MIG welding, technique is a HUGE part of it. You need to build up an appropriately large puddle of molten metal to start with. I then traverse across the joint with a sort of swirling pattern to get a nice thick weld similar to what you get from OA welding.

My first sten was built with OA, I used mig on this one because a) I have the gear and b) MIG is easier to use if you are practiced enough to know how best to use one.

[Mick]

I like magwells a lot. I'm not sure, but I think I think I may be developing an obsession

[Mick]

here are some preliminary design decisions in my quest to devise an acceptable open bolt design. BE AWARE. These design changes ARE NOT YET REVIEWED BY THE RCMP AND MAY NOT GET APPROVED. You would build and submit a gun like this at your own risk as it may get confiscated.

Here we see a steel block that has been cut to fit between the trigger box wall and the disconnector slot. Coupled with the above-detailed modified selector, the trip lever can now not be readily made to move over to the full-auto position and the steel block welded in from behind makes filing out the disconnector slot nearly impossible:

And here is the back side showing the plug weld:

Here's another way of blocking the trip lever.

[Claven2]

My open-bolt design is actually with the CFC and RCMP labs right now for approval. It's actually been with them for almost 2 months now.

Some key points are that in my version the sear pin and trigger pins are welded in so that the internals can no longer be removed for modification.

More to follow.

[tiriaq]

An RCMP approved open bolt design with an assigned FRT number is critical. Hopefully Claven2's will be accepted.
Haven't been able to find any homemade open bolt semi auto versions in the FRT to date, for Stens, Suomis or anything else.

[Claven2]

When I spoke to George Fraser last week, he indicated there are NO OPEN BOLT SEMI-STEN DESIGNS APPROVED IN CANADA - (yet).

So let's be clear - until a new FRT number is available indicating a legal open-bolt semi - I trust nobody will post photos of a completed gun matching that description.