Stens of the World, Part 2: U.S. Stens

A Sten MkII “tube gun”—this example was made by Charlie Erb, a Class II manufacturer from Pennsylvania. The original owner paid $150.00 for this Sten. The Sten is fitted with a No2 Mk2 “T-type” buttstock.

The Sten submachine gun was created out of necessity during World War II by the British, who were standing alone against the German Army. Despite its crude appearance, it is possible that the British Sten gun has been used and copied more than any other submachine gun before or since.

Although there are a few original Stens in the NFA system, most of the Sten guns in private hands today were assembled from original part kits and a new U.S.-manufactured receiver tube. According to federal law, no original receiver foreign guns could be registered after 1968, but a new receiver could be manufactured and used to assemble a working submachine gun—after, of course, BATF approval. Unfortunately, laws were passed in 1986 ending any new (transferable) registration of machine guns.

There were several versions or marks (models) of the 9mm Sten, ranging from the MkI to the MkVI. Some were limited production or experimental prototypes. The most common are the MkII, the MkV and the MkIII. The MkII variant was by far the most popular in the U.S., because of the large number of part sets available and its simple construction. Fewer MkV Stens exist, due in part to the lesser number of MkV Stens manufactured and thus fewer available part sets. The MkIII was not as popular, due to its more integrated construction.

The table is covered with Sten tubes at an English factory during World War II. Like in the U.S., the British war industry workforce was comprised of females.

The Sten submachine gun holds a certain mystique for many collectors. Perhaps it’s the weapon’s history, nostalgia or its simple but effective construction. Judging by the number of countries that copied the Sten, the respect for the crude, utilitarian weapon was widespread.

There is a fairly large amount of original and aftermarket parts and accessories available for the Sten: magazine pouches, mag loaders, caliber conversions and, on occasion, brand new parts still in their original packing. A number of different stocks and pistol grips are available, many cleverly fabricated from the plentiful T-style No2 Mk2 buttstocks.

Prior to 1986, a large number of Sten “tube guns” were made and registered by Class II manufacturers, making them readily available for anyone looking for one. During the 1980s, prior to the 1986 ban, an MkII Sten “tube gun” could be purchased for as little as $150.00, plus the $200.00 federal transfer tax. Most U.S.-made Sten tube guns were finished with a light to dark gray Parkerizing.

As stated, the most common Sten is the MkII model. Many owners of an MkII have opted to upgrade their Stens to the more ergonomic MkV model or the even more refined Sterling MkIV. Sten guns converted to Sterling submachine guns are often referred to as Stenlings.

An MkV Sten “tube gun”—few MkV models were assembled in the U.S., due to the small number of available MkV parts available before the 1986 ban on transferable machine gun production.

Original Parts Manufacturers

A question often asked by Sten owners is, “Who is the British manufacturer marked on my magazine housing?” In the case of the Sten, it’s more a matter of who assembled my gun. Individual parts (including magazine housings) were made by hundreds of workshops and companies scattered throughout England. In place of names, codes were marked on the parts to conceal their origin. The parts were then shipped to factories that assembled them into weapons. Thousands of Sten part kits were imported from different countries, so it is possible that the markings on the housing may not be British. The key to identifying who assembled an original Sten is the original serial number.

Known U.S. manufacturers of Sten receivers: CATCO, DLO Mfg, C. Erb, FAKTS, Fleming Firearms, Interport, John Stemple, Pearl Mfg, Qualified Mfg, Rubin, S&H Arms, Silver Bullet (York), Specialty Weapons, Taylor Manufacturing, Wilson Arms and York Arms.

The MkII Sten

There are several reasons for the popularity of the select-fire MkII model. The subgun is chambered for the common 9mm Parabellum cartridge. There seems to be an almost endless supply of inexpensive spare parts and magazines to maintain the gun for a long time. There are many original and aftermarket parts to enhance the Sten or to change its basic configuration. There are several original and aftermarket buttstocks and pistol grips, caliber conversions and barrels. The Sten MkII can be easily disassembled into a compact package for transport, concealment or storage, and the Sten is a good candidate for the mounting of a suppressor. The original finish on the Sten MkII varied by manufacturer, varying from dull blue-black to Parkerizing.

An aftermarket, insulated canvas cover hides the muzzle end of the modern suppressor, giving it the appearance of an original suppressed Sten MKII S. The Sten is fitted with an early production No3 Mk0 buttstock with a diagonal strut for attaching a sling.

The MkIII

The MkIII Sten was designed for two reasons: to speed up production and reduce cost. The receiver was made from a rolled piece of sheet metal welded together along the top seam. The barrel was held in front and rear supports that were permanently riveted, making the barrel non-removable. Many components, such as the magazine housing, were permanently attached to the receiver tube by spot-welding. (This solved the problem caused by the housing sagging on the MkII and MkV models.) After determining that the MkII was a better design, MkIII model production was terminated in 1943, but examples remained in military service. In recent years, large numbers of MkIII part sets have been imported into the U.S. Many of these kits have included the, formerly rare, cast bronze-aluminum alloy bolts. The MkIII parts that will fit into an MkII are the bolt, extractor, extractor pin, selector, trigger assembly, trigger pin, sear, sear pin, trip lever, recoil spring, spring cap and lock, buttstock, magazine catch and spring. Other parts, although not readily interchangeable, can be modified to work in the MkII model. The bottom line is that the MkIII part sets can be used as an inexpensive parts source for the Sten MkII.

The MkV

The MkV Sten was introduced in 1944; it cost more and took longer to manufacture than the MkII model. By 1944, the threat to the British homeland had subsided, and the urgent need for weapons had diminished. The Germans had their hands full fighting in the Soviet Union. The barrel of the MkV featured the adjustable front sight and bayonet lug of the Enfield Mk4 rifle, as well as a pistol grip. Early models had a forward pistol grip attached to the barrel retaining sleeve, but counter-clockwise pressure from a hand would rotate the grip and loosen the barrel. The model of the Sten is marked on the magazine housing. Early production MkV Stens were marked with a Roman numeral; later, this was changed to an Arabic number 5. The MkV submachine guns were Parkerized then finished with semi-gloss black paint.

A Sterling MkIV/L2A3 submachine gun made from original Sterling parts and a Sten receiver tube.

Converting a Sten MkII to an MkV

The construction of the MkII Sten differs from that of the MkV model, so a conversion from an MkII to an MkV is more complicated than just a parts swap. The MkV trigger housing was modified to house the pistol grip and is positioned 1.3 inches further forward. A conversion from an MkII to an MkV configuration would entail cutting the MkII trigger housing off, then cutting new openings in the bottom of the receiver and cutting a new safety slot (as well as welding patches over the old ones) in order to move them 1.3-inches forward. Some parts of the MkV differ from the MkII. The barrel bushing has an index pin to align the barrel, so the front sight is vertical. The tripping lever has an angle on the end, and the trigger housing cover is shorter. The front bearing surface of the bolt has a cut on the bottom to clear the tripping lever; an MkV bolt can be used in an MkII or MkIII, but an MkII bolt will not work in an MkV Sten.

Converting a Sten to a Lanchester

The Sten receiver is very similar to that of the Lanchester submachine gun. However, like for the Sterling, the cocking handle slot on a Sten tube is oriented slightly differently to that of an original Lanchester. This problem can easily be overcome by using the original Sten bolt. The Sten bolt and recoil spring also address two design flaws of the Lanchester: the firing pin and the extractor. One other problem was that the Sten receiver tube has an outside diameter that is slightly smaller than that of the original Lanchester. This results in a loose fit between the receiver tube and Lanchester magazine housing. This is addressed by installing a thin .015-inch spacer between the housing and the receiver. The perforated barrel jacket of the Lanchester is attached to the Sten tube by welding. For attachment of the original endcap, a receiver extension can be fabricated and welded to the rear of the Sten receiver. One of the major obstacles of a Sten to Lanchester conversion is a limited supply of part sets.

The basic configuration of a Sten can easily be changed by swapping its buttstock. Pictured are some aftermarket concoctions to make the Sten shorter or slightly more ergonomic.

Converting a Sten into a Sterling

The Sterling MkIV conversion turns the 1940s Sten design into a more modern, ergonomic submachine gun. The Sterling offers a well-designed folding stock, a canted pistol grip and—perhaps best of all—reliable, easy-to-load 35-round magazines. A commonality of the British Lanchester, Sten and Sterling submachine guns is the dimensions of their receiver tubes. One difference is the position of the cocking handle slot in the tube. In 1994, the Sterling was replaced by the SA80 rifle in British service. During the late 1990s, a fair number of Sterling MkIV/L2A3 submachine gun part sets were imported, and it didn’t take long before someone discovered the similarities between the Sten and Sterling. After months of correspondence with the BATF’s Technology Branch, permission was granted to use a Sten receiver tube to make a copy of a Sterling MkIV. However, the conversion is quite an undertaking, requiring a skilled gunsmith with a well-equipped shop. This is because, first, many of the components welded to the Sten tube must be carefully removed, and, second, the Sterling components—several of which are silver soldered to the receiver—must be added. This must all be performed with care, so as not to warp the tube. Alignment of the Sterling components onto the Sten tube is critical to achieve reliable functioning. To keep the conversion within BATF guidelines, the cocking slot in the receiver tube could not be changed. The problem of the Sten’s 50-degree cocking slot versus the Sterling’s 60-degree location was solved by modifying the cocking handle with a 10-degree offset. Sten magazines will fit and function in a Sterling. Unfortunately, however, Sterling magazines won’t readily work in a Sten.

Magazines

The Achilles heel of the Sten gun is the double-stack, single-feed magazine. The primary problem of the magazine is the feed lips that determine the angle of the cartridge being fed into the barrel’s chamber. The feed lips have a propensity to spread apart slightly, changing the angle of the top cartridge. If an angle of 8 degrees is maintained and there are no other issues with the weapon, it should function as designed. The British made two variants of the Sten magazines, the MkI and MkII. The MkII design eliminated the “round-count” holes in the back of the magazine housing and added a strut between the follower’s legs to keep them from spreading apart and restricting the follower’s movement. (For more in-depth information on Sten Magazines, refer to SAR Vol. 17 Issue 3, September 2013.)

A kit to convert a Sten to the potent 7.62x25mm Tokarev cartridge.

Recommended Reading

The Sten Machine Carbine
Peter Laidler, Collector Grade Publications.

Sten Parts and Accessories
International Military Antiques: ima-usa.com

SARCO, Inc.
e-sarcoinc.com/sten.aspx

Numrich Gun Parts
gunpartscorp.com/gun-manufacturer/sten/mkii-sten

BRP Corp
brpguns.com

Occasionally new-in-the-wrap Sten parts can be found. This 1946 dated, sealed box contains two brand new Mk2 Sten bolts. The Mk1 bolts were designed for the MkII Sten. The Mk2 bolts, which were designed to clear the trip lever in the MkV Sten, can be used in all Sten models.

A pile of deactivated MkV Stens for sale at the War and Peace show in England. A few are fitted with the forward pistol grip. The laws in Europe differ from those in the U.S. In many countries, the receiver is allowed to remain intact, but the barrel and bolt are modified so that the weapon will not fire. In the U.S., the receiver is the registered/controlled part.