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STEN MkIII with tight chamber causing stovepipes


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I have an original STEN MkIII with an extremely tight chamber. Unlike our STEN MkII and every other 9mm SMG we have, a round will not seat fully in the chamber. You have to push it in to fully seat it, then it needs to be levered out.

The chamber is clean and free from burrs. I get the feeling that it might have left the factory that way, as the gun is very clean and has seen little use.

Testing with Dykem shows the chamber too small near the rifling.

 

The above problem causes stovepipe jams. You can't get through a mag without dozens of jams.

 

I was debating taking a 9mm chamber reamer and trying to fix the chamber, but as the barrel is fixed in the MKIII I'd have to go through the back and use a T-handle extension - and of course the ejector is in the way. In the MkIII it's riveted in place, so I'd have to remove that rivet. Rather not do that unless I have to.

 

Suggestions anyone?

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When finish reaming the chamber on an M1 rifle, a long rod is inserted in the muzzle, the chamber reamer is fastened to the rod, and as the rod is turned the bolt is pressed down.

Makes for perfect headspace.

You need to locate a gunsmith that has such a combo for 9 M/M.

Jim C

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An open bolt SMG is not comparable to an M1 for "headspace", so all that needs to be done is to carefully ream the chamber preserving current depth with a 9 Para finish reamer to cut the chamber to a uniform diameter to the throat. A slightly loose chamber is fine in a Sten.

This assumes that the ammo is not the problem. FWIW

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Easy to use an extension with a reamer from the rear of the receiver and have done that on quite a few occasions on other types of SMGs for various reasons. An extension is easily applcable in this situation and a rather obvious solution. I probably could have been more specific though to avoid confusion.

Jim C: sorry to have misinterpreted what you were saying but it appeared to me to address a headspace issue and I was thinking about light reaming of the chamber with an extension. What you suggest would work fine, too, if one has the appropriate equipment for pulling a reamer from the muzzle end.

Edited by Black River Militaria CII
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so knock out the rivit and remove the ejector. rivit is probaly copper, fhen you cad rework the chamber.. replace ejector with new rivit, really guys dont make such a big deal about it.

 

That's exactly what I proposed. It doesn't hurt

 

When finish reaming the chamber on an M1 rifle, a long rod is inserted in the muzzle, the chamber reamer is fastened to the rod, and as the rod is turned the bolt is pressed down.

Makes for perfect headspace.

You need to locate a gunsmith that has such a combo for 9 M/M.

Jim C

 

Jim,

 

We order customer reamers and gauges all the time, the problem with a custom 9mm pull style reamer is that it would be quite expensive and based on current items we have on order would take 3 months plus to get.

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An open bolt SMG is not comparable to an M1 for "headspace", so all that needs to be done is to carefully ream the chamber preserving current depth with a 9 Para finish reamer to cut the chamber to a uniform diameter to the throat. A slightly loose chamber is fine in a Sten.

This assumes that the ammo is not the problem. FWIW

 

That's exactly what I was thinking. We've done it before on other guns with damaged chambers and it's worked fine. I'm not seeing any damage to the chamber, so assuming it is a manufacturing defect. We tried Swiss Gecco, Federal 9mm and British MK2Z and none of them would chamber properly. A 9mm headspace gauge won't go in either so that's pretty conclusive.

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so knock out the rivit and remove the ejector. rivit is probaly copper, fhen you cad rework the chamber.. replace ejector with new rivit, really guys dont make such a big deal about it.

 

Billy, not a big deal. It doesn't hurt to bounce something off of folks before doing it. For all I knew there might have been some other solution that I hadn't thought of.

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while you have ejector out ot gun check for worn, burrs or bent, is your gun one of the mk iii imported from finland,, a lot of these had new finland made barrels installed, most of the mkiii from finland had a small hole drilled fhru the stick stock for a sling swivel

 

No small hole on this one. It came with the standard T-stock. Interestingly, none of the loop stocks I have will fit, and would need material ground off of their locking lug in order to fit in place. Everything else on the gun look good - well as much as it can for a STEN MkIII.

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Something is amiss here. An original mk3 would have been test fired on numerous occasions and faults fixed at the time.

 

I suspect the barrel chamber is dirty/damaged or it is not an original barrel. Could it be an ex Indian gun?

 

All rivets appear to be original. Chamber is an clean as a whistle. We even checked with a borescope to make sure. Gun is English manufacture, no idea what country it was imported from. Might well have been India.

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