DIY MK IIS Sten Gun: The Ultimate Vintage World War II Homebuilt

The wares at our local gun emporia are beginning to look a bit repetitive, my friends. There are AR15 variants for every taste, proclivity, and budget. The counters are awash to their gunwales in plastic pistols. There’s the obligatory smattering of scatterguns, precision rifles, and wheelguns, but that really is about it.

If your interests wander to older iron the pickings get yet slimmer. Feel free to pick up a vintage transferable full auto Thompson if your surname is Trump, Gates, or Soros. However, for us normal folk affordable vintage WW2-era guns that will legitimately set you apart from your peers are just not available on the contemporary gun market. However, if you are handy with tools the determined gun bodger can craft some of the most extraordinary firearms legally at home. The obvious candidate is the Sten.

[one_half][/one_half][one_half_last][/one_half_last]

Sten Parentage

Sten is an acronym that stands for Shepherd, Turpin, and Enfield. Major Reginald Shepherd and Harold Turpin crafted this most basic of submachine guns at Enfield, England, in 1940. The British Army had only just barely survived the evacuation at Dunkirk, and Goering’s Luftwaffe was pounding English cities day and night. Isolated and alone, the English stood as a final bastion against the megalomaniacal aspirations of the Nazis and all their manifest darkness. While the British Army had miraculously crossed the channel intact from Dunkirk, they were bereft of weapons. In these darkest of days, Turpin and Shepherd designed a desperate gun for desperate times.

The Sten gun was known by a variety of epithets, none of them complimentary. The Stench Gun or the Plumber’s Nightmare both alluded to the weapon’s crude construction and Spartan design. However, the Sten was easy to produce in simple facilities and cost a paltry $9 apiece. This equates out to about $154 today. These same utilitarian attributes make the Sten a great build candidate for the modern ballistic hobbyist.

SPECS

• Semiauto Mk IIS Sten Gun
• Caliber                                   9mm Parabellum
• Barrel Length                         16 in.
• Overall Length                        38.3 inches
• Weight                                   7.75 pounds
• Magazine Capacity         32 rounds
• Action: blowback semiautomatic—closed bolt
• Sights                                    Fixed rear peep, front post

[one_half]

[/one_half][one_half_last]

[/one_half_last]

Sourcing the Components—The Parts Kit

Sarco is a foundational name in American surplus. They have for decades offered the most delightful selection of gun parts, surplus military equipment, live weapons, and sundry treasure. I am convinced that Sarco is where the good gun nerds go when they die.

Sarco offers kits and parts for dozens of guns. Their demilled Sten kits are complete save the receiver and barrel. All Sten kits available these days have seen hard use, but they yet remain all but indestructible. In the United States the receiver is the serialized portion of the gun that is controlled so this component has been thoroughly slagged. There is also an inane restriction on the importation of barrels for which we have Bill Clinton to thank. The rest of the kit is greasy and filthy but entirely serviceable.

The Magical Bits

Indianapolis Ordnance is the Skunk Works of modern gun building. These guys offer a wide range of products from 80% receivers to semiauto conversion parts to legal full auto blank-firing submachine guns. Their wares include components for the MP38, MP40, MG34, BAR, and Thompson submachine guns as well as tube receiver guns like the Swedish K, Sterling, Sten, and others. I have built several guns using their parts, and their receivers and conversion parts are both well engineered and superbly executed.

Conversion parts required for the Sten build include barrels of various flavors, reduced diameter receivers, and semiauto bolts and internal parts. A reduced diameter receiver excludes the original full auto bolt and keeps the build legal. The charging handle geometry is altered slightly as well to make the gun essentially impossible to convert to full auto. Unlike the original open-bolt submachine gun, the Indianapolis Ordnance conversion uses a closed bolt mechanism with a separate spring-loaded striker activated by the gun’s original sear.

Equipment Requirements

The first order of business is to cut the usable parts away from the previous receiver remnants. This chore succumbs readily to the patient affections of a Dremel tool. Familiarize yourself with the sundry parts before you start grinding, and take care not to damage anything significant. Try to leave any attachment tabs intact on the original parts. They’re not critical, but it is easier if you have these to weld upon later. Always wear eye and ear protection if you don’t want to end the project deaf and rocking an eye patch.

[one_half]

[/one_half][one_half_last]

[/one_half_last]

Most of the build can be undertaken with a small drill press and a Dremel tool. A hand drill would do in a pinch, but a modest drill press is much more precise. You will need to do a little welding before you’re done, but any machine shop could knock this out for a reasonable fee. I invested in a cheap wire welder from Harbor Freight Tools that is more than capable of finishing this project. Trust me, I am self-taught and truly suck at welding and I pulled it off. You can, too.

[one_half]

[/one_half][one_half_last]

[/one_half_last]

Article Continues Below

Finishing the Receiver

The receiver tube from Indianapolis Ordnance comes with a paper template bonded firmly in place. Use a spring-loaded center punch to spot the necessary holes and edges of your cuts according to the template. Then use your drill press to drill out the ends of the various slots and angled bits. The ejection port, for instance, should begin as a series of four holes, one in each corner.

Once the sundry holes are in place configure your Dremel tool with a fiber-reinforced cutoff wheel, don your safety glasses, and carefully cut the various slots and voids. If you had enough steel stock and fiber-reinforced cutoff wheels for a Dremel tool you could build an Abrams tank if you had adequate patience. Take your time and remove everything that is not a Sten receiver. Then swap out to a small sanding drum or grinding bit to dress up all your slots. Once the cutting is done it is time to fit our components in place.

Fitting

Carefully fit the trigger housing to the new receiver and make sure all the slots align. These things were just thrown together during World War 2 so there might be a bit of Dremel work required for a proper fit. A small hand file will reach the spots the Dremel won’t. Thankfully, the Sten gun enjoys broad tolerances and is subsequently remarkably forgiving.

You can harvest the front barrel bushing from your surplus kit, but it is a pain. Indianapolis Ordnance makes a modern replacement that is much more convenient. All the parts should slip right in place. The old ejector and front sight are cut from the Sarco kit, and they will have to be welded. Set the bolt in position and shim the ejector with a couple small pieces of paper to hold it in place while you weld it from the outside. That way when you remove the paper the bolt should slide freely with a little clearance. Once again, any proper machine shop could easily manage the required welding if need be.

[one_half]

[/one_half][one_half_last]

[/one_half_last]

Keeping It Classy

In the United States, a rifle must sport a barrel at least 16 inches long to remain legal. This is a stupid rule, but it was birthed in 1934 back when telephones were wired to the wall and weighed as much as a bowling ball. Indianapolis Ordnance can hook you up with the long barrel. However, in its untamed state, the long tube just looks lame.

The answer to this conundrum is to replicate the Sten Mk IIS. The Mk IIS was the world’s first operational sound suppressed submachine gun, and it was a revolutionary piece of work indeed. The famed World War 2-era German SS commando Otto Skorzeny purportedly fired off a magazine from a captured example in downtown Berlin with passersby being none the wiser.

The wartime Mk IIS consisted of a standard Mk II gun with a bronze bolt and an integral sound suppressor. To replicate the Mk IIS in your build you simply craft a barrel shroud around the ungainly long barrel. I picked up a length of 1.5-inch muffler pipe from my local muffler shop. Cut the tube to length with a cutoff wheel on a table saw or hacksaw. The tube should extend from the barrel nut to the end of the barrel.

I bodged together an end cap out of a washer I found in my shop and carefully carved the hole out with my Dremel to accommodate the barrel. Cut the original Mk II shroud that came with your Sarco kit as a base and bevels the edges with a bench grinder or Dremel. Once the whole affair is prepped weld it together into a single assembly.

Assembly and Finishing

I took a wire wheel to the whole shebang to get rid of the rust, scale, and detritus from the assembly. Degrease everything with mineral spirits and then spray it down with bake-on ceramic engine block paint from your local auto parts store. You can bake this noxious stuff in your wife’s kitchen oven if you never want another home-cooked meal. I had an old discarded kitchen oven wired into my shop to use for this purpose. A decent toaster oven from your local box store would do as well.

The Sten gun goes together fairly readily. I sewed a canvas cover out of some heavy brown cloth to replicate the cloth heat shield of the originals. So long as you had access to these basic tools the entire project can be completed in a weekend.

Range Time

The Sten magazine is a double stack design that tapers to a single feed. This means you will either need a dedicated magazine loader or a small length of dowel to get the box loaded to capacity. Start one round at a time and take your time. You will have to tweak the sundry springs to get the gun running well, but the Indianapolis Ordnance instructions show you how.

It took me about an hour carefully trimming back the twin springs one coil at a time and then firing a round to get the gun running well. Bring your wire cutters and you can accomplish this chore from the bench at your local range just be patient. Indianapolis Ordnance provides you with two spare springs just in case.

The finished gun has been reliable with ball ammo but be careful. These components are 70+ years old. I did have one out-of-battery discharge that resulted in a squib round (a bullet stuck in the barrel) while timing the springs. There was no lasting harm done, but that is the reason we religiously respect the safety rules.

The gun is surprisingly accurate given its motley parentage. The ergonomics are hideous, but the Sten was designed to save a desperate nation, not to be comfortable. The feeling I got when I first ran a magazine through this pile of parts I built myself was remarkably satisfying.

Final Thoughts

At the end of the day, I have added something truly unique to my gun collection for less than the price of a proper plastic pistol. Don’t be intimidated by the build. I am living proof that you can be an epically crappy welder and still successfully pull it off. If the welding part still intimidates you just farm it out to your local machine shop.

This is a fairly advanced home workshop project, but it demands a lot more patience than skill. Better tools would have made the build quicker and easier, but I wanted to prove to myself and you that it could be done with a drill press, a Dremel tool, and a $150 Harbor Freight welder.

The personal satisfaction of having resurrected this old gun at home with help from Sarco and Indianapolis Ordnance is tough to measure. So long as you build the gun for personal use there is no requirement under federal law to register it anyplace or even grace it with a serial number. The Mk IIS Sten project is great fun, deeply satisfying, and thoroughly cool.

For more information about Sarco parts, click here.

To purchase parts for your build, check out Indianapolis Ordnance.