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Thread: STEN failure to extract issues

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    STEN failure to eject issues

    I have recently been having problems again with my MK2 sten. I had it rebuilt by John Andrewski and for about 7000 rounds it ran nearly flawlessly but now I'm having failure to eject malfunctions again. It usually happens on the last two or three rounds in the magazine.

    I have 23 mags and four bolts and have tested all but to no avail. I have also replaced extractor springs and done some other things.

    I have also checked the weight of my action spring and it's at 13# which seems about right.

    It seems that the top round in the magazine may be bumping the case off the bolt face but I'm not certain. I have checked the feed angle on all of my magazines with the correct British gage and all of them are correct.

    I'm not sure if this is a bolt velocity issue or something of that nature as when I hand cycle a case out of the chamber with a dummy round in the magazine it falls off in the receiver if I go slowly but lazily ejects out if I run it briskly. This gun has never had strong ejection by the way.
    Last edited by m1garand_man; 07-18-2017 at 06:17 PM. Reason: mislabled the title

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    I don't think you have fully explained what malf you are experiencing?

    Is the case stuck in the chamber?

    Bouncing back in and blocking the bolt from closing?

    3 quick questions:
    How much movement and play does your mag well housing have?

    Have you checked the ejector?

    Check your chamber for rust, pitting or roughness,

    To be honest, I highly doubt that you are experiencing "extraction" issues as most mkii will function without an extractor...
    Last edited by bsn; 07-17-2017 at 12:06 AM.

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    Quote Originally Posted by bsn View Post
    I don't think you have fully explained what malf you are experiencing?

    Is the case stuck in the chamber?

    Bouncing back in and blocking the bolt from closing?

    3 quick questions:
    How much movement and play does your mag well housing have?

    Have you checked the ejector?

    Check your chamber for rust, pitting or roughness,

    To be honest, I highly doubt that you are experiencing "extraction" issues as most mkii will function without an extractor...
    Failure to eject. The bolt will strip and feed a new round but the spent casing will be stuck between the bolt face and the front trunnion preventing it from firing.

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    Hard to tell what’s wrong without seeing it. What does John say?

    A worn mag housing can do what you are describing. As the mag gets lighter there is less down force on the housing and if it is loose, it can move and the bolt can rub against the mag feed lips.

    You can check your mags for bolt rub marks. Another thing you can do is use a marker on the bolt to see if it is rubbing somewhere.

    BRP has housings if you need one. http://www.brpguns.com/categories/Pa...Housing-Parts/

    Mk2’s were plagued by loose mag housings until they were withdrawn from service. There were several attempts to fix the problem. Crimping the housing was a temporary fix. The only permanent fix was to weld the housing to tube.

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    I haven't taken a look at the bolt rubbing yet. I do know my mag housing is fairly tight but there is a slight bit of movement. I'll have to do the marker trick.

    Any other ideas while I'm waiting until my next range opportunity?

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    So I called John Andrewski again. He said that by decreasing the feed angle from the 7'35"* the mags normally have should help with prematurely kicking the brass off the bolt face.

    I went and looked at the interplay between the bolt and dummy round in the magazine again this morning and it seems that when the nose of the bolt crosses over the extractor groove in the top round in the magazine it causes it to abruptly nose up temporarily which is the point at which the empty case is kicked off. I'm not sure if there is any way to minimize this effect. But I'll know more tonight.

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    After doing some more thinking it occurred to me that possibly my magazine springs are all too weak to keep the round from tilting once the nose of the bolt crosses the cartridge rim. As noted before this malfunction mainly seems to happen during the last two or three rounds in a magazine and when I got these mags originally they had much stiffer springs. I couldn't get more than 10 rounds in them with out needing the loader. Now I can fully load some of them by hand.

    Now the next question is what other magazine springs are compatible with the sten mag body. I know I'm not likely to find an exact fit but something close will work. I'm curious to see if 33 round glock mag springs will work since they would be cheap to purchase in bulk. I would really like a high quality spring or something chrome silicon so they don't lose their strength.

    Have any of you rebuilt sten mags?

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    Quote Originally Posted by m1garand_man View Post
    ……. and when I got these mags originally they had much stiffer springs. I couldn't get more than 10 rounds in them with out needing the loader. Now I can fully load some of them by hand.
    That’s interesting. I have never heard of anyone doing that before.

    BRP has mag springs and mag loaders. http://www.brpguns.com/categories/Pa...nes-and-Parts/



    Quote Originally Posted by m1garand_man View Post
    Have any of you rebuilt sten mags?
    Can you define “rebuilt” for me?
    Last edited by Traveler; 07-17-2017 at 10:40 PM.

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    Registered User sniperdoc's Avatar
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    Are you leaving your mags fully loaded?

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    I used to leave them loaded. Not after the first few months of owning the gun when I discovered the springs had taken a set.

    By rebuilding I mean reforming the feed lips and setting the feed angle as well as installing new springs. I have the original tools to do this which I purchased from brp years ago. Apparently magazines weren't considered as expendable by the British during the mid 1900's as in the modern US army. They sent mags through the Thurough Factory Rebuild program which is probably why the forming tools and gauges for magazines exist.

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    I believe that it's highly unlikely that all your mags are bad unless you left all of them loaded for a long time.
    Try buying one or more of the new Tapco mags first.
    If that doesn't work,you know it's not the mags and can look elsewhere for the problem and save a lot of time.
    Yes,the Brits expected the mags to last.

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    If you can fully load a Sten magazine by hand either your other name is Clark Kent or your spring is shot. I note that Wolff Springs offers replacement magazine springs for the MP-40, which might work well in the Sten magazine.

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    I have loaded STEN mags by hand, but I have no clue if they would have ran in FA guns (they were for SA MPA MAC)
    I do have a greater than average hand strength, due to having to use a cane,and over 30 years of martial arts practice.

  14. #14
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    Quote Originally Posted by m1garand_man View Post
    By rebuilding I mean reforming the feed lips and setting the feed angle as well as installing new springs.
    I have taken out a lot of dents, set feed lips and welded sheaths back on. Never had a need for a new spring. Some people take the brass rods out of the 19 round ICR low friction converted mags and call it “rebuilding.” That’s why I asked.

    I have also done a few of the 7.62x25mm conversions.


    Quote Originally Posted by sniperdoc View Post
    Try buying one or more of the new Tapco mags first.
    Those are probably the worst mags I have ever had. I wouldn’t recommend them. A proper Sten spring is cheaper and it should do the trick.

    It’s strange that the gun worked with the weak springs in the mags for 7,000 rounds before the problem surfaced.

  15. #15
    Registered User sniperdoc's Avatar
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    I've never used the Tapco mags; only 2nd hand info

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    It has always had a failure to eject once in a while, maybe every 5 or 6 mags but as of late it has become more like every mag.

    So my saying I had no problems before was not accurate.

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    I would try a stock Sten mag spring first. If that doesn’t help, I would look at the fit of the mag housing. After that I would look at the barrel chamber.

    What ammo are you using?

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    I was probably going to buy some Wolff mp40 mag springs since they should work and are about half the cost of stock springs.

    As far as ammo I am using 124gr reloads that worked fine in the past and Remington 115gr factory loads.

    The chamber is perfect. The barrel was made by sa machine.

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    It's a bit of a side bar but I discovered how to minimize round tilt in some of my known bad magazines.

    Using the mag body repair mandrel and two pin punches laid in line with the rear magazine necking indentations and squeezing the magazine in a vise it causes the rounds to not tilt so much there by repairing magazines with which the nose of the bolt misses cartridge rims when the rounds tilt nose up.

    I got the idea by looking at indentations on the external surface of fome of my mags where they were probably adjusted during a factory thorough repair.

    Make sure you do this with the mandrel in however or you will likely deform the mag body.

  20. #20
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    I wish I could find a British technical manual with repair instructions for the sten. We have them in the US army. I'm surprised that Google turns up nothing useful.

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