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Thread: Sten Tube Diameter**Size** Question

  1. #1
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    Sten Tube Diameter**Size** Question

    Hey everyone im working on a sten MKIII project and I have asked this question on a few other boards and it seems im getting a few differnt answers.

    Im building a semi auto Sten MKIII and I hear that what ever company I order the tube from I have to use their semi auto bolt. Is this true?

    Does anyone know the size of the tube from Inianapolis Ordance?

    Also anyone know the size of the tube from semiautosten.com?

    I think Im going to try and get a 4130 steal tube localy and get either my own print out or one that is ready to stick on the tube.

    Here is the size tube I have been told but really would like more input.

    Length 18 1/32

    outter Diameter 1.5

    Wall thickness 0.083

    Inner diameter 1.334

    I really would like to be able to get my own tube as that will cut some cost down but without knowing what the real size is that I need and what kit will work im not sure if its worth doing that.

    Thanks everyone for your help and time.

  2. #2
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    Does anyone know the size of the tube from Inianapolis Ordance?
    Outer Diameter is the same as the original STEN, 1.5".
    The wall thickness is about 0.104.
    That means the ID would be about 1.396.

    Im building a semi auto Sten MKIII and I hear that what ever company I order the tube from I have to use their semi auto bolt. Is this true?
    No. You can use any "Closed bolt" that will fit as long as it fits inside a tube with a smaller ID than the original STEN. ((The BATF want the receiver tube ID to be smaller so the original STEN bold cannot be used. They also want the cocking handle to be relocated, bolt must be of the "closed bolt type", etc, etc.))

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    Thank you Traveler for the info man. Let me ask another question .

    So when I ask about a tube from a local source I just give them what you gave me?

    I also found this http://www.prexis.com/Merchant2/merc...tegory_Code=ST templete to use.

    will the tube need any milling on the inside to except any of the parts. I see on some of the tubes a small ring on the inside.

    I know buying the tubing is cheaper even with the drawing but if it needs stuff milled I have no way of doing that. I can cut out the holes and things like that. I just done have a full machine shop outback lol.

    Thanks for the help and the info.

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    The template looks like the cocking handle has been relocated, so it's probably OK. Check with them to make sure it's for a semi auto before you get it.

    will the tube need any milling on the inside to except any of the parts.
    Yes, if you are going to use the original STEN front barrel trunnion and recoil spring end cap retainer.

    You can get a smaller front barrel trunnion. I haven't seen a reduced size recoil spring end cap retainer.

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    Quote Originally Posted by Traveler
    The template looks like the cocking handle has been relocated, so it's probably OK. Check with them to make sure it's for a semi auto before you get it.



    Yes, if you are going to use the original STEN front barrel trunnion and recoil spring end cap retainer.

    You can get a smaller front barrel trunnion. I haven't seen a reduced size recoil spring end cap retainer.
    Traveler can you explane that to me more please.

    Im going to use the orginal barrel for a pistol build for now and later on I will buy a fake can and make a carbine.

    So if I save the front trunion (I think I can) and re-use and the original recoil spring end cap I will have to do some milling your saying.

    I think I have seen someone making new front and rear parts but I have to look again.

    Please explane it to me a bit more as im following you and I think Im getting it now lol. THanks man.

  6. #6
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    So if I save the front trunnion (I think I can) and re-use and the original recoil spring end cap I will have to do some milling your saying.
    That's correct. You need to use a lathe to bore out the ID of the front and rear ends of the tube so it will take the original STEN trunnion and end cap.

    I think I have seen someone making new front and rear parts but I have to look again.
    I have only seen reduced size trunnions, no recoil spring end cap retainers.

    The receiver tube from Indianapolis Ordnance comes with the front and rear ends bored out so you can use the original STEN front trunnion recoil spring end cap retainer. It's an 80% receiver tube, so you still have to cut out the holes for the mag well, ejection port and trigger sear.

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    Quote Originally Posted by Traveler
    That's correct. You need to use a lathe to bore out the ID of the front and rear ends of the tube so it will take the original STEN trunnion and end cap.



    I have only seen reduced size trunnions, no recoil spring end cap retainers.

    The receiver tube from Indianapolis Ordnance comes with the front and rear ends bored out so you can use the original STEN front trunnion recoil spring end cap retainer. It's an 80% receiver tube, so you still have to cut out the holes for the mag well, ejection port and trigger sear.
    I have to tell you I dont have access to a lathe and the name that keeps coming back to me for a tube is Indianapolis Ordnace.

    I have had semiautosten.com mentioned and prexis.com. The problem there is semiautosten.com email is not working and prexis kits work with their (semiautosten.com) bolts.

    I hear good about all three but Indianaplis Ordnace is the one that keeps coming back for a first time builder.

    I think by the time I cut corners to get the tube and the lathed and the templete im back up to the price of what one would be straight from Indianaplis Ordance.

    Thanks Traveler you have been a big help in this question and helping me make up my mind. I just have to save up some more then get the right parts.

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    Glad to be of help.

    I think you will be happy with Indianapolis Ordnance. Their parts are very good quality. The workmanship is excellent.

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    Quote Originally Posted by Traveler
    Glad to be of help.

    I think you will be happy with Indianapolis Ordnance. Their parts are very good quality. The workmanship is excellent.

    Thanks man I just went out and my dad and I took the barrel off and now are getting ready to tap out and or grind off the pins holding the front trunion on. Im going to a site I found how to take out the welds and stuff and see how they did it.

    Im also going to call Indianapolis Ordnance and see what I need to save or buy new. Thanks again Traveler.

    I also want to thank Ron for telling me to ask questions here and he told me I would get an anwser real will quikc and I did.

    So a big shout out to Ron for his help as well and to you Traveler.

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    Indianapolis STEN TUBE Question---- REPLY your all wrong... so still am I

    OK. So ---- reading the first post in my google search of where to buy cheap tube I went to Shaperio Supply and got 1.5 x .083 in tubing. I bought 2 feet and all said and done they conveniently charged me $15 for the tube and $15 dollars for shipping. This needless to say was $30 for two feet of tube - Lame.

    The tube arrives and sliding my IO bolt in there it was like a Hotdog in a Hallway.

    Now to see if Shapiro will give me a few pennies back for my troubles and send me a 1.5 x .095 inch tube.

    MATH FOLLOWS :::::::::

    1.5 in tube - 2(.095) = 1.310 inches
    Measured IO BOLT = 1.297 inches

    Clearance of Bolt on each side = (1.310 - 1.297)/2 = .007 inches on each side


    NOW - BEFORE I MAKE ANOTHER ILL Advised PURCHASE. is 7THOUSANDTHS of an inch on each side of the bolt much too much. I know ideally itd be .002 or so... but I have now run out of standard tube sizes.

    1.5 x .104 ------> -.004 clearance............ that is the next size. Advice????

  11. #11
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    My advice? I know this is gonna sound lame, but I would just buy the Indianapolis Ordnance tube to match the Indianapolis Ordnance bolt. You've got $30 invested in the wrong size tubing, and may have to spend another $30 to get tubing that could be wrong as well. Their tubes, with a template, are $70-80.

    I know this doesn't answer the question fully, but these are just my thoughts...

  12. #12
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    Original MK III Tube was 1.5" x 0.058" Wall. So 1.5" - 0.058" = 1.442" - 0.058" = 1.384" Tube ID.

    So are there different Size Semi Bolts? I see here 1.5" x .083" Wall Tubing mentioned and I see 1.5" x .095" Tube!

    MK III Semi is also 1.5" OD x ????? Wall?

    I found a Drawing of the MKII Bolt and it said the Bolt OD is 34.67mm = 1.365" OD. 1.384" - 1.365" = 0.019"/2= 0.0095" Clearance.
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    Last edited by Armilite; 11-14-2021 at 11:18 AM.

  13. #13
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    MKIII

    ORIGINAL MKII receiver was 38mm OD x 35mm ID. So 38mm = 1.496058" and 35mm = 1.377949" Why there is so much Slop.

    1.5" x .065" Wall. 1.5 - .065 = 1.435" - .065" = 1.37" ID. Bolt OD per Drawing is 34.67mm = 1.365" OD. 1.37"-1.365"= 0.005" Clearance.

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