This is my new Sten. There are many other like it, but this one is now mine...

Greetings all. One of my men, knowing my penchant for things British in general and WW2 weapons in particular, gifted me a Sten yesterday. It's unlike others I've seen, and has a rather interesting provenance. The man's grandfather was a commander in the French resistance and was based in the high Alpine region near the Swiss border. He was tasked at a certain point with the removal of a high ranking German officer, and obtained a weapon for the operation. This weapon, apparently, is the same Sten I now own. It is in remarkably good condition, with original black finish, and is complete with an absurdly ungainly silencer. This silencer is far larger than the models I've seen before. It is massive in diameter, unscrews from both ends, and has a rubber washer at the muzzle hole. It appears to be made of steel. The Sten itself is a MKII, and has an S stamped on the magwell. The recoil spring is shorter than on my other Sten models, and the bolt has a deeply recessed hole for the extractor pin. The rest seems the same, although the gun's finish is far finer, with all the welding smoothed out. The bolt also fits the receiver tube far more precisely. Interesting animal. I'd love to hear any thoughts about that huge silencer...
It also came with a spare barrel, and of course I had to try that out. Recently I was disappointed by one of my Stens that was grouping high and far right. This one is, to use the parlance de jour, an absolute tack driver. At 10 yards all rounds cut the same hole, and at 25 yards all rounds struck within a man's palm. These were fired seated using a sandbag as forearm rest. Pics if requested, to follow next week.

It would be interesting to see some pictures, please.

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Originally Posted by 5 Commando

I'd love to hear any thoughts about that huge silencer...

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Yes, we'll need to see it. The can could be a one off done at the time...but the gun is marked for quiet use with the "S", denoting the extras you mentioned. The accuracy is fine, you see now that they aren't all the same. The last one had issues that should just be disregarded I think... Love to see it.

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Originally Posted by 5 Commando

Pics if requested, to follow next week.

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Could you also tell us what the weight of the bolt is?

No photos, no info I'm afraid........ we're not clairvoyant

I have to wonder about the spare barrel and the fine finish, I don't remember any of the Mk2s I've looked at being any different to a normal Mk2 in finish and a spare barrel would imply that either could be used which may not be best practice with a light bolt and short recoil spring.

I'll post some pics next Tuesday. To be continued...

Attachment 82131Attachment 82130Attachment 82129

At 10 and 25 m. At 10 m barrel notch was not at 12 o' clock. 25 m result is with barrel notch at 12'o clock...

It is a small notch engraved into the barrel and apparently should be at 12 o' clock when barrel nut is tightened. I can vouch that at all other positions the poi deviation is extreme, see 10m result in previous post.

You need a horsehair and canvas cover for that bad boy. Fit and finish seems very nice. Nice gun...

That was the SOE silencer and described in the book. Your gun should never be fired on automatic with that silencer fitted. I seem to recall that the change lever was made so that it could not be moved to the A side.

Nice gun but I do have some questions, I'm not trying to tear the story apart but I just wonder if that paint finish is original. It doesn't look like suncorite and I can't see any paint missing. Compare that to the silencer and they don't match, the silencer looks spot for what I'd expect and thought the patina on the gun would match. The other thing I noticed is the breech block doesn't show signs of being lightened but I know that it wasn't always nessisary. Also the ground welds look similar to what the Finns did to their guns, non of my STEN Mk2s except the Finn gun have ground welds.

I totally agree with BP's comments regarding the two distinct finishes. Has the paint been burned off the hot silencer I'm bound to ask? They do get VERY hot! So far as the ground welds are concerned, I don't think that ground or un-ground welds on the mag housing are indicative of an S gun. More indicative of the manufacturer of the mag housing or at a particular time during the war. Ground welds were a spec. requirement later for the Mk5 guns

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Originally Posted by browningautorifle

You need a horsehair and canvas cover for that bad boy. Fit and finish seems very nice. Nice gun...

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Shouldn't need that, as the larger diameter tube is a heat shield which is spaced away from the suppressor tube.

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Originally Posted by Peter Laidler

I totally agree with BP's comments regarding the two distinct finishes. Has the paint been burned off the hot silencer I'm bound to ask? They do get VERY hot! So far as the ground welds are concerned, I don't think that ground or un-ground welds on the mag housing are indicative of an S gun. More indicative of the manufacturer of the mag housing or at a particular time during the war. Ground welds were a spec. requirement later for the Mk5 guns

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Originally Posted by Lee Enfield

Shouldn't need that

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Originally Posted by Peter Laidler

They do get VERY hot!

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Seems you're alone in that thought process...I've built and shot them. They get VERY hot. The originals had a wrap for a reason.

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Originally Posted by browningautorifle

Seems you're alone in that thought process...I've built and shot them. They get VERY hot. The originals had a wrap for a reason.

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Everyone is probably aware that they get hot, that's why the SOE MkIIS cans had this nifty spaced outer tube...theoretically removing the need for the canvas & asbestos or horse hair wrap. Not sure how effective it was, but certainly would be cooler than a Military MkIIs or MkVI can, and as repeatedly pointed out, these cans were/are not meant for full auto firing - which should significantly limit the heat build up.

Attachment 82136
Here is a photo of a disassembled SOE MkIIS can....note the inner and outer tubes.
Attachment 82138
note the (SOE ?) catalogue illustration, no fabric heat shield...
Attachment 82139
Attachment 82140
Note the Military Sten MkIIS & Mk6 can drawings, with fabric heat shields...



stolen from this excellent article
http://www.smallarmsreview.com/displ...articles=2360#

I'm a bit bemused by picture 2, para 2, that the silencer can be fitted to a standard (mk2) Sten but para 4, method, says that it cannot be used on any other gun because....... That's ambiguity at its best. It either CAN be used on any gun - or it can't! We can only assume that it is matched for bore to exit hole alignment alone.

Also in para 2 it declares that the speed of the bullet is reduced to 980 ft/sec. Quite how they achieve this by fitting a silencer is beyond me! The special notes part mentions the luminous sights. It amazed me when the radiation examiners came around with their radiac survey dosi-meters - or dosser readers as we called the users - , the meter clicked like the clappers when it got to our silenced guns. But they were right. Under years of black paint and hidden luminosity, the radium was still sound. I just assume that the radium was made and applied by Volkswagen!

My further comment on the lack of protection is that while there might well be a thermal shunt between the two 'casings', so was there on the Sterling. And that got too hot to handle after just a few rounds. We used to pull an old woolen sock, the thick army issue ones, over the casing

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Originally Posted by Lee Enfield

stolen from this excellent article

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You see, I'm not interested in borrowing someone else's article or talking about hearsay...I'm wondering how many suppressed "Things" you've handled yourself? Any?

I'm speaking about cans I've shot and handled and built. As Peter states...after even a few rounds they get hot. The Sterling (L34?) I've had here and know exactly what he's talking about. Even a Delisle has a wooden forend because even single .45's make the jacket hard to handle in a few rounds.

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Originally Posted by Peter Laidler

too hot to handle after just a few rounds.

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Anyhow, I don't need to cut and paste other's work here. I just made a simple comment about aesthetics and you wanted to take me to task. I can discuss silencers in detail...

Yep!

All of that energy has to go somewhere! '"Wet" cans are an interesting study in themselves. Otherwise, you have to get rid of the heat via the mass of the muffler itself; as it heats up, it basically becomes less efficient, because part of the way a proper can works is by essentially cooling the gases and slowing down their entry into the atmosphere.

Then again, who is likely to still be "clandestine" after expending several mags of 9mm, even with a decent muffler? The "smack" of bullets striking, even at sub-sonic velocities, is not to be ignored, never mind the rattle of the action and the "tinkling" of the spent brass.

"Silent" they ain't: the whole point is to "diffuse" the muzzle blast that is the rather distinctive signature of "normal" shooting.

SOE silencer, what a wonderful thing to have! I would agree the gun has a very Fin rebuild look to it, any SA stamps anywhere?

I'd love to have one of those myself...or a correct M3...fun for the whole family.

Thank you for posting the pictures. It’s an interesting gun and suppressor. The ground welds are consistent with other S Stens I have seen. Though I have never seen markings like that on the magazine housing. I don’t know if they are correct. All the ones I have seen have the S after the II on the top side of the housing.

The suppressor was clearly used with a thermal sleeve. The mottled spots mark where the sleeve was. I don’t see any signs of high heat… the change in colors you see when steel is heated to high temperatures.

Without seeing the internal parts I can’t tell if the suppressor is an original or a copy.

Assuming the silencer is an original SOE example, it must be a very rare piece.

With regard to the lack of S markings Vincent, was the SOE silencer designed for retrofit to a standard Sten Mk2, as required, that would fit with the nature of SOE Operations.

I don't have my Sten book to hand at the moment, but I would assume (if it was designed) for use with a standard Sten, it would come with an adjusted/modified barrel??

As far as I know, I think it's in Peters book that I read it and saw the photos, the SOE STEN had a modified selector to remove the Auto capability, that would make it non standard.

Looks like your gun is from the first batch.

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Three main types of Special Sten/Sten Mk.II(S) have been observed in quantity as follows:

First production model silencing units are found on B.S.A. manufactured guns with B prefix in serial number series B 341000, B 360000 and B 363000. The silencing units are two inches in diameter and are not equipped with any web handguards. The insulation is integrated in the silencer between the inner and outer tubes of the silencer. All the weapons observed have had the letter “S” stamped on the bottom of the magazine housing. These Sten guns are typically marked STFN instead of STEN, indicating a worn die used for marking the guns.

The silencer has a number of metal discs in front of the 7.2 inch barrel, which is ventilated with 6 bleed holes. A thick rubber disc is placed at the muzzle of the silencing unit to stop the powder gases from escaping. The effect of the silencing unit decreases as the rubber disc wears out. A number of silencing units have been observed with light bullet strikes at the muzzle, possibly caused by firing in recent times after the rubber had hardened thus diverting the bullets.

The silencing units are serial numbered and observations have been made in a range from 1-3400. It is not possible to say if as many as 3,400 were made but the observed numbers from 1-1500 have been so many that it’s quite possible that this range was filled. A number of these weapons were also equipped with night sights. Guns with night sights had the silencing unit permanently attached to the submachine gun. Most of the observed silencing units with night sights were in the 1-350 serial number range with one exception around serial number 3400. This model appears to have only been used by SOE agents. As mentioned above, these silencing units are possibly the shortened Kulikowski silencing units mentioned in the reports.

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http://www.smallarmsreview.com/displ...darticles=2360

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Originally Posted by Bruce_in_Oz

Then again, who is likely to still be "clandestine" after expending several mags of 9mm, even with a decent muffler? The "smack" of bullets striking, even at sub-sonic velocities, is not to be ignored, never mind the rattle of the action and the "tinkling" of the spent brass.

"Silent" they ain't: the whole point is to "diffuse" the muzzle blast that is the rather distinctive signature of "normal" shooting.

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Exactly the case with an M3A1 I used. It was a story wet day and still the smack of bullets at 25 yards and the jingle of brass was constant. It just wasn't loud like it would have been. And it was fun...and very hot. I had to use a glove on one hand.

That's right. there is always a distinct and unforgettable heavy dull 'thud' as the bullet hits home. Preferably into someone else of course. Difficult to describe the actual noise........ a thud like smack - but you know it when you hear it again, even when fired into a sheep carcass

The noise varied with the exact backstop. I was of course moving around a bit, rubber matt, dirt, foreground...backdrop...jingling brass and mags changing...good fun.

It was interesting to play with much later designs on 5.56 and 7.62 NATO platforms, using standard, supersonic "ball" ammo..

The instantly noticeable effect was that muzzle "blast" was subjectively reduced to something like a high-velocity .22 Rimfire; loud-ish, but not the familiar bellow of a 7.62 NATO fired without the muffler. The interesting thing was that there was a kind of "whoosh" as the bullet went down-range. This was actually the reflections of the "sonic boom" bouncing off the trees along the range border.

Down in the butts, the bullets "cracked" overhead as per normal, still being supersonic, BUT there was barely any of the "thump" of the actual discharge muzzle-blast. And these rounds were only fired from 300metres away.

These "cans" were an "experimental" co-axial design, but as with all such devices, they got VERY hot in a few shots, especially with amount of powder burnt in the "big" 7.62 NATO round. Another fun day with the 'meriCAN cousins!

One of the 5.56 versions was fitted to a VERY short-barreled toy, (think XM-177 clone).

A 30-round mag of ball was "dumped" into a tree-stump about 25 metres away. The extra mass of the muffler held the beast on target and the chips flew, accompanied by the sound of tortured timber and a fast-moving mechanism. DEFINITELY not "silent' but an impressive demonstration.

One "downside" is that, with semi/full-autos, "back-pressure", especially with co-axial cans, blows incompletely burnt powder particles back into the action. This gets things dirty, but with "open-topped" toys like the M-14, or Bill Ruger's mini version, you also need your serious shooting glasses OR one of the old "blank-firing" shields.

Furthermore, with gas-operated goodies, it is nice to be able to adjust the port pressure, (L1A1s are good for this), or you may well be "over-driving" the system, especially with "full-strength" ammo.

I have a Gemtech suppressed bolt carrier. It really reduces the blowback gas and the bolt speed. It also works great with subsonic 300 Blackout (7.62×35mm). GEMTECH 5.56 Suppressed Bolt Carrier

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Originally Posted by Peter Laidler

That's right. there is always a distinct and unforgettable heavy dull 'thud' as the bullet hits home. Preferably into someone else of course. Difficult to describe the actual noise........ a thud like smack - but you know it when you hear it again, even when fired into a sheep carcass

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There’s a strange thing about that thud sound, Peter. You don’t hear it when you’re on the receiving end. You hear the whizzing of the ones that go by, but your mind somehow blocks that thud sound when you’re hit…. so I’m told.

The military aspect was to simply remove the signature. Smoke, flash and blast. Once the location of the shooter was hidden, the supersonic crack misguided the searchers to look in different locations. It works well too.

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Originally Posted by Peter Laidler

That was the SOE silencer and described in the book. Your gun should never be fired on automatic with that silencer fitted. I seem to recall that the change lever was made so that it could not be moved to the A side.

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The change lever - at least on this piece - moves between R and A. It fires smoothly in auto mode. I note your caution about no automatic fire with the silencer fitted. I stripped the weapon entirely for inspection cleaning and lubrication. The trigger assembly is identical to other Stens I've had, with a stamped sear, but with a shorter recoil spring.

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Originally Posted by browningautorifle

You need a horsehair and canvas cover for that bad boy. Fit and finish seems very nice. Nice gun...

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I know. I've got my agents out searching as we speak!

---------- Post added at 10:20 AM ---------- Previous post was at 10:11 AM ----------

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Originally Posted by Brit plumber

Nice gun but I do have some questions, I'm not trying to tear the story apart but I just wonder if that paint finish is original. It doesn't look like suncorite and I can't see any paint missing. Compare that to the silencer and they don't match, the silencer looks spot for what I'd expect and thought the patina on the gun would match. The other thing I noticed is the breech block doesn't show signs of being lightened but I know that it wasn't always nessisary. Also the ground welds look similar to what the Finns did to their guns, non of my STEN Mk2s except the Finn gun have ground welds.

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Good points. The pics I posted may have been somewhat misleading. I chose the best angle to show off my new toy. Mea culpa. In fact the finish is original, and shows quite some wear on the receiver tube. I wondered also about the difference in patina between the silencer and the gun proper. Posed that question to the grandson who spoke to grandad and came back last night with an answer, and a rather fascinating little insight into WW2 underground operations. Apparently this silencer was heavily used by their particular unit for training purposes. This involved basic familiarization of the weapon and target shooting. The low noise signature allowed them to fire without attracting attention from ze Chermans. In doing so, the silencer was used on a number of different weapons, and aged at a greater rate than the original host weapon. Sounds plausible, as the barrel rifling is heavily worn almost to extinction.

---------- Post added at 10:24 AM ---------- Previous post was at 10:20 AM ----------

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Originally Posted by Lee Enfield

Everyone is probably aware that they get hot, that's why the SOE MkIIS cans had this nifty spaced outer tube...theoretically removing the need for the canvas & asbestos or horse hair wrap. Not sure how effective it was, but certainly would be cooler than a Military MkIIs or MkVI can, and as repeatedly pointed out, these cans were/are not meant for full auto firing - which should significantly limit the heat build up.

Attachment 82136
Here is a photo of a disassembled SOE MkIIS can....note the inner and outer tubes.
Attachment 82138
note the (SOE ?) catalogue illustration, no fabric heat shield...
Attachment 82139
Attachment 82140
Note the Military Sten MkIIS & Mk6 can drawings, with fabric heat shields...



stolen from this excellent article
http://www.smallarmsreview.com/displ...articles=2360#

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Thanks for the amazing pics. I had scoured the net but never came close to something like this. Very fascinating, and saves me from stripping the beast to look inside, although how long can resist that remains to be seen...

---------- Post added at 10:33 AM ---------- Previous post was at 10:24 AM ----------

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Originally Posted by Bruce_in_Oz

Yep!

All of that energy has to go somewhere! '"Wet" cans are an interesting study in themselves. Otherwise, you have to get rid of the heat via the mass of the muffler itself; as it heats up, it basically becomes less efficient, because part of the way a proper can works is by essentially cooling the gases and slowing down their entry into the atmosphere.

Then again, who is likely to still be "clandestine" after expending several mags of 9mm, even with a decent muffler? The "smack" of bullets striking, even at sub-sonic velocities, is not to be ignored, never mind the rattle of the action and the "tinkling" of the spent brass.

"Silent" they ain't: the whole point is to "diffuse" the muzzle blast that is the rather distinctive signature of "normal" shooting.

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Interesting observations. At a point to be determined I will be taking chrono speed readings using subsonic 9mm. I will also film the firing operation and make a sound file with studio quality decibel recordings. In the process I plan on measuring the suppressor's heat rise with my handy infra red device that is usually employed to check if the coals are ready for my pizzas in the outdoor oven. I think the data on this silencer should be put on record for prosperity.

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Originally Posted by mrclark303

SOE silencer, what a wonderful thing to have! I would agree the gun has a very Fin rebuild look to it, any SA stamps anywhere?

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Sorry, my mind must be slipping. Correction, it is slipping. Remind what SA stamps are?

---------- Post added at 10:35 AM ---------- Previous post was at 10:34 AM ----------

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Originally Posted by browningautorifle

I'd love to have one of those myself...or a correct M3...fun for the whole family.

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Exactly. My thoughts exactly. The family that shoots together...

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Originally Posted by Vincent

Thank you for posting the pictures. It’s an interesting gun and suppressor. The ground welds are consistent with other S Stens I have seen. Though I have never seen markings like that on the magazine housing. I don’t know if they are correct. All the ones I have seen have the S after the II on the top side of the housing.

The suppressor was clearly used with a thermal sleeve. The mottled spots mark where the sleeve was. I don’t see any signs of high heat… the change in colors you see when steel is heated to high temperatures.

Without seeing the internal parts I can’t tell if the suppressor is an original or a copy.

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I guess a strip-down is in the future then...

---------- Post added at 10:39 AM ---------- Previous post was at 10:37 AM ----------

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Originally Posted by Vincent

Looks like your gun is from the first batch.



http://www.smallarmsreview.com/displ...darticles=2360

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I had missed the small detail about the worn die. Rechecked the piece and indeed it is so. You guys are an amazing resource.

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Originally Posted by 5 Commando

Remind what SA stamps are?

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Sometimes the Fins marked their weapons with their ownership mark of "S.A." but not always.

SA = Suomoi Army. Or Possibly 'Armee'....:)

I think I'll eat my hat now. That article really proves this STEN as an early genuine gun. One thing this thread has raised is that the manuals are ambiguous stating in para that the guns are standard and then in another that they are specially converted. I think I know what they were implying but that's not how it should have been written.

I don't think that there's any need to back pedal BP. You've said what I've been thinkin'. I've been pondering this for several days now.......... The more I look at this gun scenario now, I'm thinking that the gun is in fact a standard Mk2 Sten. Fair enough. And the silencer and barrel assembly is/was not originally with the gun but they came together later, for reasons best known to 'someone'.
The SOE Stens I saw (and I only examined 3 or so) had distinctly lightened breech blocks as opposed to this standard - or barely lightened - if at all - breech block. And all had definately restricted change levers without the auto fire facility. Standard Mk2 gun fitted with an SOE silencer from another OR one dropped/shipped in for a one-way-trip job!

I'm no expert here but have seen a few hundreds and having a basic grasp of the mechanicals and physics of it all that's what I think. But like I always say, I could be wrong

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Originally Posted by Brit plumber

…. That article really proves this STEN as an early genuine gun….

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I think the magazine housing is genuine.

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The E.S.6(W.D.) SOE design utilized a deeper chamber where the bolt would make contact with the breech end of the barrel before the cartridge was fired, so the chamber pressure in full could be used to work the bolt to the rear. This design allowed the use of a standard bolt and recoil spring in the silenced Sten and a theoretical use of the silencing unit in any Sten Mk.II available. In practice the SOE silencing units also had reliability issues.

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The deeper chamber seems to explain the standard breech block. But it also supports Peter’s thoughts that it’s a standard Mk2.

The magazine housing makes me think it’s an authentic “S”.

Mmmmmmmmmmmm not too sure of that para commencing 'The ES6(WD)..... '. Where did that statement originate Vince? I ask due to the principle of advanced primer ignition which is just a by product of a fixed firing pin in a blow back weapon. And guess what the Sten used? Yep, all 3!

Some silenced Stens had a radium filled dot drilled into the rear of the foresight blade and a similar radial filled saw-cut across the centre line of backsight. Not all, but a good starting point. Even if the radium had been removed the dot and line will be visible. Mind you, so will the radium for the next 200 years or so. Id did make the radiac survey meter click like a clapper box. But there again, so did my old Omega wristwatch!

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Originally Posted by Peter Laidler

Mmmmmmmmmmmm not too sure of that para commencing 'The ES6(WD)..... '. Where did that statement originate Vince?

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It came from this article http://www.smallarmsreview.com/displ...darticles=2360

If I am understanding the deeper chamber concept correctly, it would reduce or eliminate advanced primer ignition. The breech block would be in contact with the barrel and at rest where the fired cartridge starts to move the breech block back.

Maybe 5 Commando can verify the deeper chamber?

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Originally Posted by Vincent

it would reduce or eliminate advanced primer ignition. The breech block would be in contact with the barrel and at rest where the fired cartridge starts to move the breech block back

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The cartridge is always at rest when it fires...if it wasn't then why would chamber depth be critical? If you run a ream in and deepen a chamber by a few more turns your weapon will no longer function...API is balloon juice...theory...

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Originally Posted by browningautorifle

The cartridge is always at rest when it fires...

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Yes, in this the cartridge is at rest. But we are talking about the breech block, not the cartridge.

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if it wasn't then why would chamber depth be critical?

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In my limited experience with blowback SMGs the chamber depth is not very critical. There’s no headspacing.

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If you run a ream in and deepen a chamber by a few more turns your weapon will no longer function...

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Most of the blowback SMGs I am familiar with have short chambers that leave quite a bit of the cartridge case unsupported.

I have made just about every mistake you can think of while making guns. One was to use the spec for a semi-auto that has a much deeper chamber than the full-auto version of the SMG. To my surprise, it shoots fine.

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API is balloon juice...theory...

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I never thought of it as a theory, just an application of Newton’s laws of motion.

There’s a mathematical analysis in volume 4 of George Chinn’s book “The Machine Gun”. https://www.milsurps.com/content.php...eorge-M.-Chinn)

My first experience converting an open bolt SMG to closed bolt didn’t go well because I didn’t really understand Newton’s laws of motion. I didn’t know a considerable amount of mass needed to be added to the bolt when going from blowback with API to plain blowback. I was lucky. The lugs on the buttstock stopped the endcap from hitting my face. After doing some research I added more mass (we can just call it weight) to the bolt, a stronger return spring and all was good. That experience made me a believer.

I can also attest to the rule of not adding water to a big tank half full of concentrated acid… a TIG welder can give you a nasty electric shock… sneakers will not protect your feet if you’re welding and a big globs of molten steel fall on them… pulling the handle down on a drill press really hard can make the drill bit snap off and it can go a long way into your forearm… if you’re extending the prongs on your wife’s Taser, it’s a good idea to take the batteries out first… a Taser (like the one my wife has) really can make you wet your pants… you don’t need a lot of gasoline to start a bonfire.. don’t fall asleep on the bank of a drainage ditch if you’re hunting hogs at night, big poisons water snakes really will try to stay warm by snuggling in with you…

I follow all of the last paragraph...very closely. I have a couple more, like Black Powder doesn't burn progressively when lit by hand. Never eat ice cream with a knife...

The blowback V?S API blowback, I take it you had a lighter than issue bolt? That could unhinge your receiver. I was wondering what firearm that happened to? I used a stronger than spec spring set on an M3 and it ran like and Ingram...that was spectacular. Harder to hang onto though.

The primer of an SMG has to fire before the bolt hits the breech of the barrel and if the firing pin hasn't done by then you're hoist, so a chamber depth is critical. The ones a bit less supported can burst if you have a dirty chamber, I have the casing remnants from a C1 SMG from the '80s. The cartridge has stopped moving forward, the bolt is still travelling forward. I had problems with an old 1928 Thompson barrel and when another ran a ream in to "freshen" it up, it would swallow the cartridge, and I watched him work. Believe me it was nothing much. It wouldn't fire after. I have other examples too...

Headspacing is the distance from the mouth of the casing to the face of the breechblock where the cartridge is seated against it. So it does exist...but there will be variables. I built up an AR in 9mm recently and chambered the barrel a bit deeper than the original...as long as the case is sandwiched solidly between the bolt face and case mouth it will be fine too...

The sfaety factor in the API guns is the forward momentum of the heavy bolt. That has to be stopped before the bolt can start rearward and during that time the pressures have dropped...

I remember we had a three pager on this one other time. I stayed out of it that time.

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The blowback V?S API blowback, I take it you had a lighter than issue bolt? That could unhinge your receiver. I was wondering what firearm that happened to? I used a stronger than spec spring set on an M3 and it ran like and Ingram...that was spectacular. Harder to hang onto though.

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It was a Mk4 Sterling bolt I was converting to semi-auto, like a Mk6 bolt. It was actually a bit heavier than a standard Mk4 bolt. The firing pin spring retainer I made was very light. So the total recoiling mass was considerably less than a Mk6 bolt with its heavy steel spring retainer.

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The sfaety factor in the API guns is the forward momentum of the heavy bolt. That has to be stopped before the bolt can start rearward and during that time the pressures have dropped...

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My understanding is stopping the forward momentum of the bolt uses energy. So there is less energy available to send the bolt back. This allows a lighter bolt to be used.

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Originally Posted by browningautorifle

I follow all of the last paragraph...very closely. I have a couple more, like Black Powder doesn't burn progressively when lit by hand. Never eat ice cream with a knife...

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Ouch!

I like knives. I don’t know why they don’t like me. Especially the ceramic ones.

The issue of chamber depth is another one of those "mysteries". In a gun like the Sten, the cartridge has to be "restrained" somehow, long enough for the bolt to move forward far enough for the extractor to start engaging at almost the same time the fixed striker is acting on the primer. The catch is that the base of the round has to be "held" until the recessed bolt-face moves forward to surround it and for the fixed striker to engage the primer, unlike in your basic auto pistol. The case head cannot do this until it is effectively fully chambered and thus concentric with the barrel and the bolt-face recess.

The 9mm Parabellum is paradoxically "the latest thing" whilst also being introduced in 1902.

It has a slight, but visible body taper, as one would expect for its age and initial use in pistols; Georg Luger's little gem springs to mind.

The taper was probably employed so that once the toggle "broke" and the case had "cracked away" from the chamber, very little effort was required to fully extract and eject it.

Meanwhile, across the big pond, some bloke named Browning had, in 1902, developed a somewhat similar cartridge, the .38 ACP, not to be confused with the later, smaller, .380 Auto.

The .38ACP, and its "hot-rod" cousin, the .38 Super, have an essentially parallel-sided case.

Browning's "next big thing", apart from sundry rifles and shotguns, was the .45ACP and its "delivery system", the M-1911 Auto pistol. This cartridge has a whole .003" included taper on its body.

It seems that the "case-mouth step" on the chamber of the Browning-designed barrel is more of a "cone" than a "step". The design and specs of the pistol also seem to have allowances for pistol component and ammo "variations".

Modern, commercial barrels all seem to have a "conventional" step. The original .38 Auto / .38 Super, are vaguely "semi-rimmed" and have virtually no "step" in the chamber. The engagement of "rim" and chamber is so small, that the rather beefy extractor is probably doing most of the work. Most modern .38 Super chambers are cut with a "proper" step at the front, not unlike a 9mm Para. See also; 9 x 21 and 9 x 23.

Note that the "classic" blow-back SMGs have a fully "surrounded" bolt-face. If they didn't have this feature, as the case head was sliding across the bolt face during feeding, pistol-style, it would snag on the fixed striker and everything would stop. All those "duly-papered and taxed" manufacturers/armourers who have "jacked-up" an Uzi pistol into a "Micro-Uzi", so beloved of action movie directors, will know what I mean. A LOT of engineering work was involved for something that appeared, in action, on screen for just a few rather visually dramatic seconds. It was “exciting” enough with movie blanks; I would not be keen to try it with 2Z ball..

Congratulation 5 Commando! Your Sten is Beautifull!!

Is my dream, Is my nightmare having or reproducing a sten gun. Specialy the Sten MK V !

Enjoy your Sten!

Regards!

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Originally Posted by Vincent

My understanding is stopping the forward momentum of the bolt uses energy.

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Agreed...

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Originally Posted by Vincent

It was a Mk4 Sterling bolt I was converting to semi-auto

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So since I'm understanding it was firing from a closed, forward bolt, therein lay the problem...nothing to lock it. I'm not surprised at the smack, I don't like the 1927A1 Thompsons available in semi auto these days that fire from a closed bolt. It gives .45 an almost unpleasant recoil...for a little cartridge.

That whole API thing implies the cartridge is fired while it's still going forward...yes, the bolt certainly IS still in motion. Hope that isn't what we're going on about...

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Originally Posted by browningautorifle

That whole API thing implies the cartridge is fired while it's still going forward...yes, the bolt certainly IS still in motion. Hope that isn't what we're going on about...

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The cartridge can be fixed, as in a blowback SMG, or moving, as in a Oerlikon cannon. All that matters is the bolt is still in forward motion. The bolt is the mass that has to be stopped before it is sent back. The energy expended in stopping the mass (bolt) leaves less energy to send the bolt back. With less energy available to send the bolt back, the bolt can be lighter.

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Originally Posted by Bruce_in_Oz

The .38ACP, and its "hot-rod" cousin, the .38 Super, have an essentially parallel-sided case.

Browning's "next big thing", apart from sundry rifles and shotguns, was the .45ACP and its "delivery system", the M-1911 Auto pistol.

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One of my favorite pistols is a blinged out .38 Super 1911. Chrome plated with gold grips. Mexicans love it… the Border Patrol belt buckle not so much.

Some people say all 1911’s are same and all ARs are the same… until they shoot a Les Bear and an LWRC.

I wont go into the complexities of the API working principles. It will bore those who understand it, & TBH.
I don't really have the time today!....

BUT!.......There IS a difference in chamber depth for Blowback SMG's/ Carbines that fire from an open bolt.
And closed firing semi only carbines/ look alike SMGs.
It is VERY easily proved!.........Albeit a Dodgy way of showing this!.......(This is Info ONLY. & I am NOT endorsing/ advocating that any of you do this!)

If you have access to a 'standard' sterling SMG of any of the variants in Select fire. Instead of putting a magazine in the housing & firing ONE round.
Insert a live cartridge in the chamber, & squeeze off that ONE round. Locate the empty case & look at it!!!!
You WILL see that it has a large Bulge near the base! This will look like a bottle neck, with a LARGE belted bulge! I have done this in service a few times to demonstrate to service users. The dangers of attempting to fire in this manner!

The round should ALWAYS be loaded & fired from a Magazine! As this is part of the cycle & execution of the complete API Firing system!!!

Closed Bolt firing Semi's operate completely differently. & to that end, the case NEEDS to be supported as completely as possible. During the Ignition Stage of the Pressure curve, during the firing cycle.

WARNING! Service Ammo such as the British MK2.Z 9mm round. Has sufficient case wall thickness to withstand the above situation description. (In most cases!)
COMMERCIAL 9mm Freely available. Will have thinner walled cases, & metallurgical properties that are mostly Variable. To that end, I again URGE you. NOT to attempt to try what I have described above!

**** The information is Technical Advice, & I do NOT advocate anyone on here to attempt to replicate the above procedure!!!!****

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Originally Posted by Vincent

The cartridge can be fixed, as in a blowback SMG, or moving, as in a Oerlikon cannon. All that matters is the bolt is still in forward motion. The bolt is the mass that has to be stopped before it is sent back. The energy expended in stopping the mass (bolt) leaves less energy to send the bolt back. With less energy available to send the bolt back, the bolt can be lighter.

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I understand all that. What I said is bunk is the actual firing of the cartridge without it being chambered, as in the bolt and cartridge are still moving(both)when the cartridge magically fires. That's an impossibility with a fixed firing pin. I'm not speaking of the Oerlikon. It's a different animal. Just things like Sten, Sterling, M1A1 Thompson... The rest of it I understand... Even the part about the chamber depth. The closed bolt weapons don't have any way for the pressures to drop like the open bolt does. That's why the new 1927A1s have such a different recoil and pressure marks on the case. Yes we too taught not to chamber a single round in the SMG C1 unless emergency (battle). The designer could have left the name of the action at blowback...because it's correct... Then there's retarded blowback as in the Thompsons with the Blish lock...which again didn't do much.

What we've got in these latter pages is 3+ days of the Shrivenham advanced design syllabus. What would be really interesting is to get all these comments written up and presented to the class. Some wouldn't stand close scrutiny as-read of course, with a bit of fuzzy logic thrown in but when discussed in the class/student group they'd make VERY good food for thought. Great discussion material. But from what I've learned, these groups (and maybe even the courses.....) don't run now. More's the pity I say

I wondered if you would surface this time Peter, the last time you spent so much verbal effort I feared you wouldn't bother. I didn't mean to get so involved...Vincent and I should meet in a middle ground and discuss this over a BBQ...Nevada comes to mind...providing it's a full auto state.

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Originally Posted by browningautorifle

Vincent and I should meet in a middle ground and discuss this over a BBQ...Nevada comes to mind...providing it's a full auto state.

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Oh, NV absolutely is a full-auto state. There are machine gun rentals in Las Vegas and Reno.

PM me and we work it out.

Nevada.........., suits me fine too. Tell Brian at BDL when and we'll meet up! It's only 2 inches away from SC according to my atlas!

Make it December as I'm there with work.

---------- Post added at 09:38 AM ---------- Previous post was at 09:38 AM ----------

And I'll show you some serious weaponry!

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Originally Posted by Peter Laidler

Nevada.........., suits me fine too.

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Originally Posted by Brit plumber

Make it December as I'm there with work.

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Would that ever be neat...milsurps convention...

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Originally Posted by tankhunter

If you have access to a 'standard' sterling SMG of any of the variants in Select fire. Instead of putting a magazine in the housing & firing ONE round.
Insert a live cartridge in the chamber, & squeeze off that ONE round. Locate the empty case & look at it!!!!

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I just happen to have a Mk4 Sterling…… so with full safety precautions taken, I tried this.

https://www.milsurps.com/images/impo...pi20left-1.jpg

The one on the left was inserted into the chamber and the one on the right was magazine fed.

It’s hard to see in the picture. The one on the left is slightly more budged than the mag fed round.

The circumference of mag fed round bulged .004” and the inserted case .006”. So, half that and you get the amount the case wall bulged, .002” and .003”.

Both cases are the same height and .001” shorter than unfired cases.

Notice how the inserted case doesn’t have the clear shiny ring at the base. Any thoughts on that?

My thoughts, without starting a fight...because I've DONE it as well many times... It works just fine. There was no perceptible difference in recoil, shot placement or cartridge appearance. The book was specific not to EVER do it, but it didn't blow anything up or destroy anything.

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Originally Posted by Vincent

Notice how the inserted case doesn’t have the clear shiny ring at the base. Any thoughts on that?

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Complete cartridge obturation of the chambered cartridge.

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Originally Posted by browningautorifle

The book was specific not to EVER do it,

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People put a lot of rubbish in the book. Then they get upset if you don’t follow their ridiculous rules. We had a “WARNING”, don’t do this!! In the next revision, they removed the warning and made it the procedure that had to be followed. So, I asked why they made the change and was told “nobody was following the book.” Then they got upset with me for reminding them of the old saying, “Nonsense breeds noncompliance.”

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Complete cartridge obturation of the chambered cartridge.

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Oh. Thanks.

Why does the mag fed case have the more shiny ring?

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Originally Posted by Vincent

Why does the mag fed case have the more shiny ring?

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Bit of guesswork there, suspect the round just settling in the chamber is not being hammered as hard as the round fully seated.

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Originally Posted by Vincent

People put a lot of rubbish in the book.

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In our case, the Small Arms cell of our Infantry School writes the pubs about weapons handling. I was posted there at the time we were improving the interim pubs on the current family of weapons and I listened to some of the deep thinkers and their reasoning. Simple things like doing a complete unload of the C6(MAG) before changing the barrel...the weapon was designed to change in mid stride. Weapon fires, stop, change barrels and weapon goes on. Just a safety catch in between...nope! We have to go through bells and whistles to change barrels...

The books were written by men that had or have very little complete understanding of firearms...like having slave labor writing a book. You get what you get and spend ages trying to change it.

There's way more to that story but it will have to wait until we're sitting across a BBQ from each other to tell...

I recall being given the lo-down on the reasons why Aust and NZ remove the barrel on the Steyr every time there's a 'show clear'. Some of the reasons left me speechless.........

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Originally Posted by Peter Laidler

I recall being given the lo-down on the reasons why Aust and NZ remove the barrel on the Steyr every time there's a 'show clear'. Some of the reasons left me speechless.........

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I have never seen that here. Just bolt locked open, mag removed and a visual inspection.

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Originally Posted by Peter Laidler

Some of the reasons left me speechless.........

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There were many things...many... Like I say, it would take a bit of time sitting around the BBQ to get all this stuff aired. Then we'd all just be frustrated.

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Originally Posted by Brit plumber

Make it December as I'm there with work.

And I'll show you some serious weaponry!

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When in December?

Looks like it's now Feb 2018 because the weapons aren't ready.

Woodsy is very probably correct in that it's not done in NZ (thread 62). One our Aust DS told us it was their drill so I just assumed that it'd be both Aust and NZ.