One of the many things that seem to interest firearms owners is caliber conversions. Often, the conversions are desired to enable the shooter to fire less expensive ammunition. During the recent “ammo shortage,” .22 caliber rimfire conversion kits became very popular. Another reason shooters like to change calibers is to experience a different “feel” in their weapon. Whatever the reason, many machine gun shooters are drawn to caliber conversions.
A Brief Sten History
During World War II, the Sten “machine carbine” was Great Britain’s answer for an inexpensive weapon that could be manufactured in large numbers in a short period of time. By 1941, the British were no longer able to afford the expensive U.S. Thompson or the indigenous Lanchester. The desperate, cash-strapped government needed an effective, but cheap weapon to arm its troops. The solution to the problem was the utilitarian Sten. The Sten was made in several guises; the most widely produced was the Mark II model, with an estimated three-million manufactured. According to Captain Peter Laidler, British armorer and author of the excellent book The Sten Machine Carbine, the name Sten was derived from the creator’s last names; Colonel Reginald Shepherd and Harold Turpin and the last two letters representing England. The Sten continued to serve in a number of Third World countries long after World War II had ended. The simple design could be easily copied and manufactured by nations having limited industrial capacity.
The British Sten Mark II, 9mm submachine gun was reproduced in fairly large numbers by U.S. Class II manufacturers prior to the 19 May 1986 government ban on manufacturing. The guns were built from original surplus part sets, using a newly manufactured receiver: these are commonly called “tube guns.” The Sten is very popular today and remains one of the least expensive submachine guns on the market, although they have increased dramatically from their pre-1986 retail price of approximately $250. Original Sten guns are far less common and generally cost substantially more than a “tube gun.” Original Sten guns qualify as Curio and Relics, while “tube guns” do not.
During World War II, the Chinese received a number of 9mm Sten MKII machine carbines under Canada’s Mutual Aid Act. Those Sten MKIIs were manufactured at Canada’s famous Long Branch Arsenal. The weapons destined for China were similar to those made for the British and Canadian armies except that they were marked with Chinese characters on the top of the magazine housing. The markings translated to: “Sten hand carry machine gun, Canada manufactured.” The bottom of the magazine housing retained the standard Long Branch markings, in English, normally located on the top of the housing.
During the late 1940s, the Nationalist Chinese began to manufacture their own version of the Sten designated the Type 38. The 9mm Type 38 was similar to the British and Canadian MKII model except it had no semiautomatic feature, a front sling swivel was added and the sheet metal housing covering the trigger mechanism had a triangular, rather than rounded, shape.
Since the 1920s, China had been embroiled in a civil war between Communist forces led by Mao Tse-tung, and the Chinese Nationalist Party led by Chiang Kai-shek, the conflict continued through World War II. The struggle finally ended in 1949, with a Communist victory. During the conflict, all of the Nationalist Chinese arsenals, and many weapons, were captured by the Communists.
With mainland China under Communist influence, they began adopting, and eventually with technical assistance from Russia, began manufacturing Soviet pattern weapons. The ammunition used in Soviet weapons was also imported and eventually manufactured in-country. Despite the influx and local manufacture of weapons, there were still not enough small arms to equip the large Chinese Army. After decades of fighting, China had collected a potpourri of small arms. Most of the weapons were chambered in a number of different calibers making the supply of ammunition to troops in the field a logistical nightmare. The ever resourceful Chinese decided to solve the problem by converting their collection of weapons to the standard Soviet cartridges of the era; for pistols and submachine guns, it was the 7.62x25mm.
The 7.26x25mm Tokarev Cartridge
The Russians first adopted the Tokarev round in 1930 for use in their Tokarev TT-30 and TT33 semiautomatic pistols. The cartridge was copied directly from the German 7.63 Mauser round. The 7.62×25 Tokarev became the standard Russian pistol and submachine gun cartridge during World War II. Its popularity became more widespread after the war, when many European countries came under Communist influence, and adopted both Soviet designed weapons and ammunition. The standard Soviet 7.62x25mm round features an 85.8 grain full metal jacket projectile. The bottleneck cartridge cases on ComBloc 7.62x25mm ammunition were originally made of brass, but copper washed or lacquered steel cases were adopted, to conserve critical metal (brass). The Communists produced tracer, armor piercing and armor piercing incendiary rounds, but these are seldom encountered in the U.S. Some of the cartridges have projectiles made of mild steel; again this was done more to conserve material (lead) than to create an “armor piercing” bullet, despite what the media reports. The projectile’s velocity can exceed 1,600 feet per second when fired from a 10-inch submachine gun barrel, and has a very flat trajectory.
Back in the 1990s, inexpensive kits were available to convert the popular British Sten Mk II submachine gun to fire the Soviet 7.62x25mm cartridge. (See SAR Vol. 5, No. 1, October 2001 issue.) The kits were originally fabricated by the Communist Chinese who wanted to standardize their weapons, many of which had been supplied by their Western World War II allies, to ComBloc calibers. Since the 7.62x25mm round is too long to fit in a 9mm Sten magazine, a modified Type 54 (the Chinese version of the Soviet PPS43) magazine was used. To adapt the magazine to the Sten, the rectangular portion of the Sten magazine housing was cut away, and replaced by a Type 54 housing welded to the remnant of the Sten housing. The standard Sten bolt was modified to work with the Type 54 double feed magazine. The cartridge base measurements of the 9mm Parabellum and 7.62x25mm cartridges were close enough so that no alterations to the bolt face were required. The Chinese conversion, kits like many surplus items that were once common, are now an item that is seldom encountered.
The primary problem encountered with the Chinese conversion kits was that to install the modified magazine housing, the front sight had to be removed. Most Stens have their front sights welded in place. This made the conversion problematic for most who didn’t want to remove the weld primarily because it would damage the finish, and because most Sten front sights won’t stay in place for long without welding.
While the Chinese conversion kits are few and far between, there is a now a new and better solution for those wanting a 7.62x25mm conversion: Sten magazines that have been reconfigured to accommodate the longer 7.62x25mm cartridges. This was done by removing the concave rib at the rear of the original Sten magazines and welding a steel plate over the cavity. The magazines are stenciled on the back 7.62×25. There is a good reason for this and it applies anytime 7.62x25mm barrels are anywhere near 9mm cartridges. A 9mm Parabellum cartridge will chamber in a barrel chambered for the 7.62x25mm round. HOWEVER, a 9mm bullet will not fit down the small bore of a 7.62mm barrel without causing severe damage to the firearm and the shooter.
Instead of the previous method of removing the front sight and exchanging the magazine housing and bolt, all that is needed are a few converted magazines, a 7.62x25mm barrel and lots of ammo. Although the original Sten recoil spring will work, it will eventually be damaged by the increased recoil of the 7.62 round. To solve the problem, there are special springs available that are designed specifically for the 7.62 conversion. The barrels, while still somewhat scarce, could easily be fabricated by a qualified gunsmith.
Despite their reputation, Sten magazines are reliable if a cartridge angle of 8-degrees is maintained by periodic inspection and adjustment. Double stack, single feed magazines are difficult to load by hand, and Sten magazines are no exception. The bad news is that the 9mm British magazine loaders, that make loading almost fun, will not work with the longer 7.62x25mm rounds.
The standard Sten sights are not calibrated for the flat trajectory of the 7.62 ammo, but this generally does not present a problem for most owners, who tend to fire their Stens in more of a point and shoot style. The report and felt recoil of a 7.62x25mm Sten immediately makes the shooter aware that the weapon is not firing 9mm ammunition.
While the supply of surplus 7.62x25mm ammunition seems to come and go, it is currently available and less expensive than 9mm. Most of the ammo is berdan primed and corrosive, not a concern if you clean accordingly. The abundance of this ammunition has created some new conversions; one of the most popular is for the AR-15. Recently, Wise Lite Arms introduced a semiautomatic version of the British Sterling in 7.62x25mm.
Cartridge Comparison(in inches unless otherwise noted)
|Bullet Diameter||Bullet Weight||Average Velocity||Base Diameter||Overall Length||Energy foot-pounds|
|7.62x25mm||.307||85.8 grains||1,492 FPS*||.388||1.370||425 ft-lb|
|9mm||.355||115 grains||1,250 FPS*||.392||1.169||399 ft-lb|
Sten magazines converted to 7.62x25mm
on an exchange basis.
PO Box 258
Boyd, TX 76023
Special recoil springs for the 7.62x25mm conversion
Scott Andry Machine
108 Beaufort Road
Fremont, NC 27830
(919) 242 6334
PO Box 847 Monroe, NC 28111
|This article first appeared in Small Arms Review V14N6 (March 2011)|