Help zeroing my Sten

All. I have acquired a Sten MKII that is quite innacurate. At 25 yards poi is about 15 inches high and to the right of poa, but with tight grouping. I have rotated the barrel (original in extremely good condition with sharp rifling) but at 90° rotation points there is no improvement. The rest of the weapon is in nice condition and functions perfectly in all other respects. What would cause my Sten to be so off? I've fired a few others and never had such deviation. Is there anything that was done with these guns at the armourer level to correct such a deviation?

Shoot it with UK/NATO Mk2z ammunition and then come back and tell us how it shoots. 15" high at 25m is so far removed from reality to he true

You're right, that should have read 15cm. I'm shooting Fiocchi 123gn and it cycles fine with that...

Further to the issue which may help with the trouble shooting. I took out the innards of the weapon and boresighted it at a point 25 yds away. The barrel does indeed point high and to the right of the sights. So it now seems as if the barrel is on skew. Beginning to wonder if, by a process of illumination, the trunnion is the problem here.

A higher front sight would deal with the elevation. Shift the sight to the right to move the point of impact to the left.
Is the front sight welded in?

It is welded, and quite convincingly so. Not sure what is an acceptable level of accuracy for the Sten, but 15-20cm at 25m seems excessive to me.

If you go out to the range and adopt a standing, waist shooting position...using short bursts of three or four...you'll soon find out what the acceptable accuracy is. Also you'll get pretty good at instinctive shooting. Hard to say what's happened to the gun over the 70 odd years... Put the ruler away, it's an SMG. Wartime production...

Could the problem be an eccentrically bored barrel? This was quite common and I had a chapped and machined Bren barrel showing the end elevation about 6" rear of the muzzle showing how eccentric it was. In armourers terms, we marked the BEST radial position of the barrel with regards to 'accuracy - such as it is - with a chisel mark at 12o'clock. The Sten barrel seating is soft soldered in position and rivetted. They did work loose but it was an easy fix.

Worth pointing out to you 5Commando that it's not a case of whether your Sten works and functions on commercial ammo. It may well do. But it cannot be zeroed using it. It was made to operate etc etc on UK Mk2z ammo. Try this

I think we're talking about 4 or 5 " group at 25 yds...that's fine for an SMG too...

If we take a step back here, what was the acceptable/expected semi auto accuracy of a Sten in Service guys, I would assume it was a MOA based at 50yd range??

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Originally Posted by browningautorifle

I think we're talking about 4 or 5 " group at 25 yds...that's fine for an SGM too...

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It's more in the 7 - 9 inch range based on 50rounds fired sitting using sandbags. I do come from the dark side (HKs) where this is definitely out of specs.

I'll need to dig out the Sten EMER but zeroing would be at 10 or 25 yards. Certainly nothing over that. I mean........ how do you zero a Mk3?

Yes sir. Note your remark on the ammo. I cannot easily source Mk2z so am going to work with what I can get.

Regarding eccentricity. Not sure if this is what you mean, but I ran a crude test on the barrel by rotating it in the trunnion and it appears to rotate evenly when sighting down the bore from above. By evenly I mean it didn't appear to the naked eye to deviate around the long. axis.

I do observe the following however: when fully seated, the base of the barrel appears to be visibly higher in the trunnion on the right side. This would - in my mind - support why it is hitting to the right. The vertical deviation I suspect is normal if the weapon is sighted in at 100 yds. Here a photo...

Attachment 81503

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Originally Posted by Peter Laidler

Could the problem be an eccentrically bored barrel? This was quite common and I had a chapped and machined Bren barrel showing the end elevation about 6" rear of the muzzle showing how eccentric it was. In armourers terms, we marked the BEST radial position of the barrel with regards to 'accuracy - such as it is - with a chisel mark at 12o'clock. The Sten barrel seating is soft soldered in position and rivetted. They did work loose but it was an easy fix.

Worth pointing out to you 5Commando that it's not a case of whether your Sten works and functions on commercial ammo. It may well do. But it cannot be zeroed using it. It was made to operate etc etc on UK Mk2z ammo. Try this

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Yes Browningauto/Jim. Good advice. Amazing how accurate instinctive shooting is. I ran 3 mags dry using short controlled bursts. Wanted to check that the mags were good, but also see if it cycled properly and using a chrono, what the cyclic rate was. All came in exactly on spec with zero malfunctions. My target results were much the same as firing supported in semi mode - high and to the right, but with obviously greater dispersion. You're exactly right, it is hard to know what happened to the gun the past 70 odd years, but she is in remarkable good condition with an excellent barrel. So remarkable that I wonder if her innacuracy spared her useful life...

It certainly looks as though the barrel is not seated squarely. There was a Canadian cutter contraption that would resurface the barrel seating square with the mechanical axis of the tube but we never had such a thing in UK service. Our EMER simply states that accuracy should be fired at 25 yards over the firing bench, forearm rested on a sandbag and using single shots. 2 warming shots into the bank followed by 7 shots at a 1" black square. 6 out of the 7 shots should fall close to the point of aim! So much for accuracy

Thank you sir. Good and bad news then I suppose. Had hoped you would have come up with a solution that involved the judicious application of a hammer blow on one of the sides of the trunnion. Just kidding. Not really. Would that work? Or ye olde Dremel to lower one side? I know, grave rolling in full swing here...
Thanks for the data on accuracy testing. Love that close to point of aim criteria. Minute of Nazi then.

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Originally Posted by Peter Laidler

It certainly looks as though the barrel is not seated squarely. There was a Canadian cutter contraption that would resurface the barrel seating square with the mechanical axis of the tube but we never had such a thing in UK service. Our EMER simply states that accuracy should be fired at 25 yards over the firing bench, forearm rested on a sandbag and using single shots. 2 warming shots into the bank followed by 7 shots at a 1" black square. 6 out of the 7 shots should fall close to the point of aim! So much for accuracy

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Originally Posted by 5 Commando

Not sure what is an acceptable level of accuracy for the Sten, but 15-20cm at 25m seems excessive to me.

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From my limited experience, I would agree. That seems excessive.

My MkV Sten is comparable to the Mk4 Sterling in accuracy. It’s not quite as good as the Sterling, but it’s close.

The Sterling instructions for zeroing also give the standard. It’s a MPI of 64mm (2.5”) at 25m. So, about 6.4cm at 25m.

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I do observe the following however: when fully seated, the base of the barrel appears to be visibly higher in the trunnion on the right side. This would - in my mind - support why it is hitting to the right.

Had hoped you would have come up with a solution that involved the judicious application of a hammer blow on one of the sides of the trunnion. Just kidding. Not really. Would that work? Or ye olde Dremel to lower one side? I know, grave rolling in full swing here...

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It looks like you have found where the problem is. I would not hit it with a hammer or Dremel it. The first thing I would do is check the barrel fit before the barrel nut is tightened. If tightening the barrel nut is canting the barrel, you would probably want to replace the nut.

I can’t tell how tight your barrel is in the trunnion. If it’s loose, you can knurl it lightly to get a tighter fit. A little hand knurler works well for this. Use lots of oil.

StenParts.com has new barrel nuts and bushings if you need them.

Swiss made RUAG 124gr is pretty close to the old Mk2z ammo.

Do not use any Pakistani surplus 9mm. It’s not reliable and you run the risk of damaging the barrel.

So, I pulled out my CAMT handed to me by an old SNR NCO when I was in mortar PL back in about '76. The spec for zeroing Sten is... "25 yds, 5 shots fired, group should be 2" above POA." There's more about PV but who cares? It further states that... "A trained man should be able to group all five shots into a circle of 3-1/2" radius."

We shot SMG C1 at 100 yd but it's an SMG, not really meant for distance. Group size would be x4 for 100M...

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Originally Posted by Peter Laidler

It certainly looks as though the barrel is not seated squarely. There was a Canadian cutter contraption that would resurface the barrel seating square with the mechanical axis of the tube but we never had such a thing in UK service. Our EMER simply states that accuracy should be fired at 25 yards over the firing bench, forearm rested on a sandbag and using single shots. 2 warming shots into the bank followed by 7 shots at a 1" black square. 6 out of the 7 shots should fall close to the point of aim! So much for accuracy

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Thanks for the info Peter, as a matter of interest what would you regard as an acceptable accuracy for a MK2 Sten at 25 yds and what sort of grouping can be achieved at 50yds?

Going with what our CAMT states, the group would be X2 for the acceptable size. IE, 3 1/2" X 2 is 7 inch group...or at 100 yds would be 3 1/2 X 4 =14" group...that's a lot.

Now, I don't know what the EMR states or the UK AMT for the Sten Machine Carbine...

Thanks Jim, going by that, if someone was going to reach out and say hello with a Silent Sten and hoping to do this with a single shot, he would need to get rather close!

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Originally Posted by mrclark303

a Silent Sten

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As I've understood and read...the idea isn't sniping at any distance but reaching over the last 20-30 yds distance. Anyone that's ever stalked men knows that the last few yards are the most dangerous because of the difficulty in being invisible... The idea of suppression is to just reach the last few yards to avoid being discovered. The smaller bullets, even .45 don't hold the smack they should at distance...

Escape and evasion was always a good exciting exercise for that BAR. Being evaders, even on a 2 day exercise is always a bit frightening I found especially when the 'enemy sentries' are close. Certain people still do these exercises on the downs around here where the local farmers, landowners, game keepers etc etc act as the eyes and ears for the directing staff. Or so I am told you understand.........

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Originally Posted by Peter Laidler

Certain people still do these exercises

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We did too, and some got out of hand.

I have shot Stens back to 100y, semi auto, prone, with a forearm rest. More accuracy than often assumed. A friend broke three clay pigeons @ 100y with five shots with a Mk. III.
First time my wife shot my Mk. II (she had very little prior experience shooting anything), it was at 25y on a silhouette target. Five singles, then short bursts for the balance of the magazine. 27 hits.

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It would be easy enough to try a different barrel, see if that affects zeroing.

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Originally Posted by tiriaq

More accuracy than often assumed.

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Make no mistake, we had part of the rifle team that specialized in SMG. They could accomplish fantastic things with a SubGun. The Sten would be no different, I owned a LB 1943 issue and it was fine. My Thompson's were great too. I hit the 200 yd steel gong first try with a shoulder fired MP38 on single rounds.

I just don't see the point in guys getting too wrapped around a lack of accuracy in a particular SMG...

With respect to appropriate ammunition to use in a Sten, consider the coned breech on the barrel. A lot of the cartridge case is unsupported. Some cartridge cases have thinner case walls close to the solid head. Badly bulged or ruptured cases can result.

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Originally Posted by tiriaq

Badly bulged or ruptured cases can result.

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Um...that's not what the problem is here...at all...

Earlier it was suggested that correct ammunition was recommended. This post is just a follow along to that one. There is more to recommend the use of correct ammunition than zeroing.

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Originally Posted by tiriaq

correct ammunition was recommended.

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Absolutely...

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Originally Posted by tiriaq

I have shot Stens back to 100y, semi auto, prone, with a forearm rest. More accuracy than often assumed. A friend broke three clay pigeons @ 100y with five shots with a Mk. III.
First time my wife shot my Mk. II (she had very little prior experience shooting anything), it was at 25y on a silhouette target. Five singles, then short bursts for the balance of the magazine. 27 hits.

---------- Post added at 10:48 AM ---------- Previous post was at 10:44 AM ----------

It would be easy enough to try a different barrel, see if that affects zeroing.

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I tried another barrel - same result. Would seem to conclude that the problem lies with the trunnion.

---------- Post added at 06:31 PM ---------- Previous post was at 06:28 PM ----------

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Originally Posted by browningautorifle

Make no mistake, we had part of the rifle team that specialized in SMG. They could accomplish fantastic things with a SubGun. The Sten would be no different, I owned a LB 1943 issue and it was fine. My Thompson's were great too. I hit the 200 yd steel gong first try with a shoulder fired MP38 on single rounds.

I just don't see the point in guys getting too wrapped around a lack of accuracy in a particular SMG...

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I agree completely, but in this case I'm seeing a definite diversion from the norm when I compare with other Stens of the same mark....

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Originally Posted by 5 Commando

I'm seeing a definite diversion from the norm

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Yes we are...my Longbranch shot just fine.