TFB Armorer's Bench: STEN Mk2 Build - Removing Old Receiver Remnants

Welcome everyone to the TFB Armorer's Bench! This series focuses on home armorer and gunsmith activities to help you improve your skills and maintain your firearms. Today, we're diving into what's essentially part 3 of my STEN Mk2 build series. If you missed the earlier installments, part 1 covered cleaning Cosmoline with an ultrasonic cleaner, and part 2 tackled converting 20rd STEN magazines back to 32rd. This time, we're getting into the real meat of the build - removing the old receiver tube remnants from a parts kit.

Note: Before anyone gets too excited about this project, I strongly recommend reading through this entire build series before making any purchases. STEN parts kits aren't the bargain they used to be; semi-auto conversion parts have gotten expensive, and this process requires patience, basic machining know-how, and comfort with power tools. This isn't a step-by-step "how-to" guide - it's how I approached my first STEN build, complete with the learning curve that comes with it.

More Armorer’s Bench Content:

• TFB Armorer's Bench: Using RCBS' Ultrasonic Case Cleaner-2 for Brass
• TFB Armorer's Bench: Cleaning Cosmoline With an Ultrasonic Cleaner
• TFB Armorer's Bench: Remington Sportsman Cleaning Kit Review
• TFB Armorer's Bench: RCBS Ultrasonic Case Cleaner 2 – A Closer Look
• TFB Armorer's Bench: Mounting an Optic on an X-Frame Revolver

TFB Armorer's Bench: STEN Mk2 Build - Removing Old Receiver Remnants

Here, we at TFB hope to inform, entertain, and even inspire any would-be gunsmith or armorer out there. Ideally, with the information I provide and with the help of our sponsors, you can have some useful knowledge pertaining to the conservation and improvement of firearms technology while at the same time sharing experiences and teaching each other new tips and tricks along the way in the comments. Digging deep into what it is to be an armorer or gunsmith has significance but what is important is what those people do to show they’ve earned that title. I am happy to share my experiences and knowledge and hope it is informative!

Make your personal safety a priority:

1. Practice proper gun safety. Always make sure before the firearm hits your bench that it is unloaded and safe to be handled.
2. Wear the proper safety equipment. The main one would be safety glasses (decent ones) since parts are often under spring tension and you may work with high RPM tools. Other honorable mentions would be latex gloves or a respirator when working with potentially harmful solvents and oils. Also hearing protection when working with loud machinery or test-firing firearms.
3. Modifications, alterations, and customizations will void your firearm’s warranty 9.5 times out of 10. Please take that into consideration before attempting any at-home gunsmithing.
4. If you are unsure about proper safety practices, disassembly procedures, or warranty standards, stop, put down the tools, and consult a competent gunsmith.

Why I'm Building a STEN

Full disclosure, I've never built a STEN before this project. I saw a fellow student tackle one back in gunsmith school years ago, but this is my first hands-on experience. The timing isn't great for this kind of project either. Parts kits that used to be dirt cheap are now commanding pretty hefty prices, and the components needed for semi-auto conversions have gotten expensive too. But curiosity got the better of me, especially after finding that most online resources were either incomplete YouTube series (probably taken down due to platform policies) or forum posts where people were troubleshooting problems or showing off successful builds. I saw a sub $400 STEN MK2 kit and jumped on it, knowing it was a hefty price for a box of cosmoline-coated jagged parts.

I do have a book on STEN construction from back when these kits were plentiful and cheap, but it's from an era when you could either legally build machine guns without the current restrictions, or it's meant for dealers. Those days are long gone unless you're a properly licensed SOT dealer.

Understanding the Challenge

When you get a STEN Mk2 parts kit, you're dealing with a receiver that's been cut up or torched to comply with import regulations. The fire control housing (think "lower receiver" in AR-15 terms, though this isn't actually the serialized firearm part on a STEN) still has chunks of the original receiver tube welded to it in three key locations:

two spots on the side wings of the trigger assembly area and one point up top, just in front of where the rear peep sight is.

Tools and Approach - Removing Old Receiver Remnants

My weapon of choice for this job was a hacksaw, backed up by a hand grinder with cutting discs for precision work. That’s right! The handy dandy Dremel is making its debut on Armorer’s Bench, much to my chagrin. Get used to it, it's sort of a fitting requirement for this cobbled-together tube gun.

You may also need a solid vise, pliers, a flathead screwdriver, a drill press with various-sized bits, a large brass punch, files, and sandpaper for cleanup.

The core objective is simple: cut out all the old receiver tube material so you can install a new one. Simple in concept, less simple in execution.

Tackling the Fire Control Housing

I started by making relief cuts just in front of the welds on those side wings, giving myself room to maneuver. Once I had the front chunk of tube isolated, I could grab it with pliers and work it back and forth until the metal fatigued and snapped off.

Then I cut behind the wings as well, leaving tabs of old receiver material still welded to the wings themselves.