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STEN Armorer's Tools and Gauges for Magazines


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Hello All,


I live in the USA and just recently acquired my first STEN MK2. It was assembled by Fazakerley under their Dec 1941 contract according to Peter Laidler's book. Trying to learn all I can.

When doing a function check the first time, I only had one mag fed reliably. Problem with other mags was Failure to Feed. Interior of bad mags were clean and deburred, follower in good condition. Guessing it must be the presentation of the cartridge? I am considering purchasing a STEN mag Go Gauge I've found but wondering if anyone knows how to use it?

I also have an armorer’s mag repair tool that includes a mag insert and mandrel that goes over the feed lips. When using this tool, should I simply tap lightly on the end of the mandrel with a hammer? The mandrel is only about 1/2 the width of the feed lips. Would I center the mandrel over the feed lips or use it on the upper or lower area? Or perhaps do two adjustments, to the upper and the lower in two steps? Laidler's book mentioned the feed lips should be parallel but I found a measurement listed on another forum that states the feed lips should be 0.360 near the mouth of the case and only 0.330 at the rim of the cartridge in order for the cartridge to be presented at a 7-8 degree angle.

Any help/advise would be greatly appreciated.

Thanks, Scott C.

STEN armours tools.jpg

STEN Go Gauge.JPG

Sten Mag Lips correct dimensions copy.jpg

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Additional info on the Failure to Feed issue. I've noticed when using the mag loading tool, that the magazine that feeds without errors also loads without errors. Every round is easily dropped in and pushed down. With all my bad mags, I experience issues loading the mags too. The problem is that when using the loader, some rounds (the base of the cartridge) fail to insert underneath the feed lips. When the happens, the round essentially ejects out the back side of the loader. I've attached two pics to demonstrate. One is a properly loaded error free mag with cartridge and the other demonstrates the problem mags not inserting under the feed lips. It doesn't happen on every round. But happens very frequently, perhaps every 2nd or 4th round?

 

btw, I can manually load rounds in the bad mags so that all are under the feed lips but I still experience FTF problems when trying to run the gun. This occurs even if I only load 15-20 rounds per mag.

 

Lastly, with all mags, when cartridges are loaded, all 9mm rounds are presented at 7-8 degree angle.

 

Any insight from more experienced STEN users will be greatly appreciated.

 

STEN Good Mag.JPG

STEN Bad Mag.JPG

Edited by imageaudio
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I've also noticed that the top horizontal portion of the feed lips is longer on the mags that don't load or function consistently. Also, the concave line that runs along the back side of the mag is flatter on the malfunctioning mags. I've attached a picture and referred to the concave portion as dimpled and flat. I would think that all the used mags I've purchased would have functioned properly at one time so it seems unlikely that I would need to file/grind material off the feed lips so guessing that length is not an issue. But maybe I need to re-dimple the back of the mags? Perhaps the cartridges are sitting too far back at the moment they are at the top of the mag? I suppose this point could wear out over time? I've attached a pic of the spots where the cartridges are polishing the back of the mag dimple. The malfunctioning mag is on the left with the longer polished point. It's hard to tell by the picture but that polished point is actually flatter and presents more of an area for rubbing to occur.

 

Just trying to figure out what is causing the problems. I've used my armorer's mag tool to tune the feed lips on the malfunctioning mags and I believe they are at the correct angle and the cartridge presents itself at an 8 degree angle. I've also swapped the follower & spring from a functioning mag and this did not correct the problem. And the follower/spring out of the malfunctioning mags worked correctly in the mags that don't exhibit the problem. So the issue appears to be something with the shell of the mag and not the follower, spring, etc.

STEN Mag feed lips differences.jpg

Mag wear points.jpg

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Well, STEN mags were notoriously "finicky". I have had a couple hundred different mags, and probably a dozen STENS Here over the years ( Plus 3 or 4 I made) as well as a M11/9 converted to STEN mags . Best trick is to get a box of mags, find the ones that work, and sell those that dont. You can try tweaking them, but sometimes there is just a combination of tolerances that make things not work. Line up of ejector, bolt, mag well and how you hold the gun all can conspire to cause problems. Mags can also be worn out, Yours do not appear to be, but they may just plain be out of spec. when you say you get F t F, what is happening ? photos would help there. ( great pics so far by the way) Are the mags stopping the bolt on a round in the magazine, jamming the bullet into the barrel extension, bolt dragging and not going bang ?

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Thanks RKI for your reply. The FTF actually strips a cartridge out of the mag but does not feed it properly into the chamber. In every instance, the unfired cartridge ends up jamming between the bolt and the barrel. When this happens, it is done with enough force to push the bullet further into the casing. In some instances, it appears as if the nose of the bullet has been dented by hitting half way between the breech end of the barrel and the bore wall if that makes sense? See attached pictures.

STEN bullet set back.JPG

STEN dented bullet.JPG

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Do you have any dummy rounds to experiment with? Have you tried stopping parts over between mags? I'd be tempted to strip your good mag down, Mark each part so you know they are from the same good Mark and swop parts over. Strip a Fail to Feed mag down, clean it fully, reassemble and try again. If it's still a no go, swop out the platform with the good one. Still a no go, swop back and try the spring. If still a no go check the mag body for any burs or ware that may bind the spring. Trying to fix a mag body is almost futile, the mandrills are good but not much use for repairing/setting the feed lips. Good job they made millions of mags.
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Thanks m3bobby. I have tried the tests you suggest. In summary, spring and followers work perfect from any mag in shell of mag that works. Spring and follower from good mag does not function in mags that don't work. That should mean it's the mag shells that are creating the issue I believe unless I'm missing something. Pretty sure it has something to do with the feed lips at this point as the issue persists even if I just load a few rounds in the bad mags.

 

I've purchased a STEN mag go gauge and hoping that will help identify any problems with the feed lips. Problem is, I can't find anywhere on the net that explains how to use it correctly. Anybody have directions for the Go Gauge?

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Also, I have purchased some additional surplus STEN mags and awaiting their arrival. Considering cleaning the cosmoline out using a bucket of gasoline. Any reason I shouldn't use gasoline for finish, etc?

 

I'm a non-smoker and will do it outside in a well ventilated area, etc so please, no jokes. I considered using mineral spirits but at $15 a gallon and gas is about $3 a gallon, figured gas is the cheaper method unless there is an issue? Please advise.

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Nothing wrong with using gas to clean them. The mags can be finished in various ways, suncorite, park, blues, browned or just in the white. The gauge is a profile gauge. Put a round in the mag, put the profile gauge on the back of the mag and see if the angle of the round matches the profile of the gauge. If not, it needs adjusting.....which can be easier said than done.

 

Also check the fit of the mag in the mag housing, the mag shouldn't be sloppy or else it won't matter how perfect the profile of the top round is as the slop will alter the angle when fitted.

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There can also be problems with the feed area of the barrel especially if the gun had been reactivated? It's not always the mags and can be a combination of both, so there are a lot of variables. I've fixed/repaired welded barrels and gotten them to run much better than just replacing it with a "NOS factory" barrel. Generally crazy, but I just couldn't bear to toss them away?

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