Sten Machine Carbine
The Sten machine carbine, also known as the 'Plumber's Delight', the 'Woolworth Gun', or less flatteringly the 'Plumber's Abortion', was an 9x19mm submachine gun used by British forces during World War 2. It is generally considered to be one of the worst guns in history due to its extreme inaccuracy and tendency to jam; its only true redeeming virtue is that it can be cheaply and easily mass-produced.
Many hundreds of thousand were made. The following "Marks" were produced :
- Mark I :
- Mark I* :
- Mark II :
- Mark II S : (Silenced)
- Mark III :
- Mark IVa & IVb : (made for special units during World War 2 and were shorter than the usual Sten only about 2000 were produced)
- Mark V :
- Mark VI S: Mark V with a moderator.
For the more anal among us the official designation was THE STEN MACHINE CARBINE, Mark II. 9mm.
The Sten will fire all 9-m.m. ammunition of the round nose rimless type. The gun is charged by blow-back and return spring. It may be fired automatically or in single shots - always fire dry. Sights are fixed for use up to 200 yards. It can also use 50 round magazines from the Lanchester SMG issued to the Royal Navy.
Weight:- Carbine without magazine 6 lb. 10 ozs. Empty magazine 10 ozs. Full magazine with 32 rounds 1 lb. 7 ozs. Rate of Fire:- Cyclic about 525 rounds per minute. Rifling:- Six-groove right-hand turn. Magazine:- Box type Mark II. holds 32 rounds. Magazine is fixed in housing on left side and held by spring-loaded catch. Sights:- Inverted V foresight, aperture back sight. Dimensions:- Length of Carbine overall 2 ft. 6 in.
Make sure the gun is unloaded, double check magazine and press breech block forward.
Butt:- Push in return spring housing, slide butt off with a downward motion.
Move forward return spring cap and housing roughly 3/8 in. and turn about 3/16 in. anti-clockwise; this frees the cap lugs from their ports in the casing. Remove housing cap and spring. Withdraw breech block to rear, remove cocking handle when in line with safety slot, put cocking handle in front of breech block, pull back and clear.
Undo barrel nut catch, turn magazine housing to the left, undo barrel nut and remove with barrel.
Turn gun upside down and then:
- Take out screw and washer on either side and then lift cover.
- Disengage trigger spring from trip lever pawl and trigger.
- Take out trip lever pawl.
- Drive out sear axis pin and disengage sear.
- Pull out change lever split pin, and holding trip lever clear, take out change lever.
- Disengage trigger axis pin.
- Extract trip lever with trigger facing forward.
- Trip lever can be disengaged from trigger by extracting trip lever pin.
- Turn gun upside down.
- Replace sear (bent back) and fit sear axis pin.
- Replace trip lever to trigger.
- Assemble trigger and trip lever with shortest arm of trip lever upwards.
- Put in trigger pin and engage short end in right plate. *Fit trip lever notch to sear.
- Pull trip lever away and assemble change lever and split pin.
- Re-assemble trip lever pawl to pawl pin on sear with long arm pushing against lower side of trip lever.
- Hook ends of trigger spring to trigger hook and short arm of trip lever pawl.
- Re-assemble cover screws and washers.
- Place in casing with cocking handle recess in line with port.
- Pull trigger and push breech block forward.
- Move cocking handle to safety slot and push forward.
Return spring in housing
- Replace return spring.
- Replace housing and cap.
- Fit cap so that the lugs fit into the ports.
- Push forward and rotate clockwise to engage, release and allow cap to go back into position.
- Lift barrel nut catch.
- Refit barrel.
- Before screwing barrel nut tight, release barrel nut catch so as to enable it to engage barrel nut. Barrel nut to be screwed tight by hand only.
- Push in return spring housing with top of butt plate and press butt upwards into position.
Important: Take infinite care with stripping or assembling. Do not force parts into position, as this causes burrs and strains, which in turn cause stoppages, and may cost you your life and possibly the lives of your comrades.
Put gun at Safe, fit the loaded magazine, pull cocking handle from Safe, and let breech block move forward until held by sear. The gun is ready to fire. For one shot fire, push in end of change lever marked R. For firing automatically, push in end marked A. Double check change lever position by pressing in the desired direction. before pressing trigger.
Double ejection, causing breech block to jam; bad functioning of magazine may also be a cause.
Shell case not ejected.
Carbon accumulating on face of breech block may stop firing pin from firing cap.
Burst or flawed case
Due to back-fire caused by dirty chamber where round is fired when not fitting snugly into same.
Cock and put to safe. Take off magazine. Remove obstruction. Replace magazine. Start firing. If this does not rectify the stoppage, change magazine and clean face of breech block.
Important: Keep magazine clean. Make sure magazine cap is engaged when inserting. Remove platform, if it sticks knock the end against the knee and replace magazine.
DescriptionThe box type magazine is the Mark II, which consists of case, platform, spring, bottom plate and bottom plate retainer. The latter is fitted to the spring, on it is a raised projection which sticks through the hole in the bottom plate.
Stripping & Assembly
Press down bottom plate retainer and move off bottom plate. Take off spring and platform. Refit in reverse order.
How to load with Mark II
Fix filler to magazine so that the spring catch engages port in back of magazine. Hold magazine upright, put the four fingers of the left hand on the lever, placing third finger through the hole in lever, resting first finger on the toe. Press down tail, putting a bullet into aperture with right hand, cap first. Lift lever with third finger and again press down to insert next round, repeat operation until magazine is filled (32 rounds). To prevent Magazine Spring from becoming weak after constant use, never load with more than 26 rounds.
How to unload
Hold magazine with left hand and eject bullets with right thumb.
The gun was designed to operate dry (without oil). Oil should only be used to preserve the rifling in the barrel when not in use.
This gun must be fired dry
When firing keep your fingers clear of the ejection opening. Always keep a firm grip of the gun. If held loosely, the gun will tend to fire high.
Wrap gun in oily rags and keep in a wooden box. Avoid using rag with loose ends as these may be caught up in the mechanism.
Forward movement, single shot
When depressing trigger, the sear is released from engagement with bent of breech block. Breech block moves forward by action of compressed return spring. Trip lever is pressed down by bent which releases it from the sear, which then rises by means of the extended trigger spring. Moving ahead, double horns on breech block meet base of cartridge and move it forward into the chamber. The extractor clips in the recess in base of cartridge and the firing pin strikes percussion cap and the charge is fired.
Rearward movement, single shot
After firing, part of the expanding gases force the breech block to the rear whilst the empty case is retained by the extractor. The ejector meets the base of the cartridge case and throws it through the ejection port to the right of the gun, at the same time the return spring is compressed by the breech block moving to the rear, and the breech block is prevented from returning (by expansion of the spring) by the sear.
When the change lever is set to A, the trip lever is cleared from the path of the bent on breech block, causing the sear to be held down and, therefore, the gun continues to fire automatically, until trigger pressure is released or magazine empty.