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Thread: Suomi Drum / M11 (RO) Conversion

  1. #1
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    Suomi Drum / M11 (RO) Conversion

    This is a continuation of the RO/BETA C Drum Magazine Conversion Pics thread. It is a brainstorming thread for those of you interested in converting the Suomi M31 drum to work with the Mac series of firearms.

    Please read the above, and following threads for some background info on this project.

    http://www.uzitalk.com/forums/showthread.php?t=5344

    http://www.oa2.org/forums/viewtopic....er=asc&start=0

    A big thanks goes out to Uzitalk user "strobro32" who initially started this mess and to all who have and who will contribute.
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    Suomi Conversion V2.0- Change to compound angle for feed tower.



    Here you can see the line I drew to show the angle of the feed tower.


    This is looking down into the magazine. You can see the spacer used to keep the rounds single stack. It is welded only to the feed lip on the drum with the upper end tapered to allow the rounds to feed up into the feed lips.

    Also, it doesn't show the forward angle of the feed tower, but it is only about 2 degrees.



    Problem 1:
    The rounds are bunching at the point where they transition from the drum to the tower. There is a lot of space in this area which seems to be allowing the rounds to become offset with one another, similar to how a double stack magazine works. I'm going to use JB Weld to build up a wedge to hold the rounds down and keep them all in line.


    Problem 2:
    The rounds sit flat at the top of the magazine. When attempting to chamber a round, it is slamed straight into the feed ramp and stops cold. I'm not sure if I should bend the feed ramp up or not. All of my other magazines have the rounds pointing up a bit and they never hit the feed ramp.
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    Quote Originally Posted by vegasSMG
    Both the C&S Metal Werkes and Vector Uzi Suomi drums conversions I owned had a strip of nylon attached around the inside edge of the drum to give the rounds a smooth slippery surface to ride on. There's a lot of spring tension in these drums and the bullets can gall on the inside of the drum's meal surface.

    There was also a forward and side cant on the feed tower which I suspect helps in the transition of the bullets as they change direction as they move from the drum to the tower.
    Thanks for the info on the nylon strip around the inside of the drum. That would prevent the binding that I see on my drum. I am still going to start with JB Weld to see if that helps the feeding through the transition area. If it does, I'll go with nylon or Teflon for the liner.

    The angles on the tower can't be more than 2 or 3 degrees forward and 2 to 3 degrees right (looking at the face of the drum). I doubt that the forward tilt of the tower will affect the feed angle of the rounds and it may not matter. From the pics I've seen of the BETA C mag conversion, the rounds are also flat so I may just adjust the feed ramp a bit to get them to feed.
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    Another BIG thanks to 9mmsubgun-m11!










    Last edited by strobro32; 04-10-2017 at 07:25 PM.

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    I actually started the project just last week myself. Since I don't have any steel mac mags yet I used a very modified sten mag for my tower. Here's what I have so far.

    forward angle of the tower. dummy rounds seem to feed good from tower to chamber. Medphy's, you may need more angle here. I think that's why your rounds are being slammed downward.


    cant of the tower. I tried to follow the angle of the fingers in the drum.


    the fingers in the drum. Mine don't seem to be binding as much but feeding to the tower still seems a bit slow and I'm not sure it will keep up with automatic fire.

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    Looks good!

    Maybe somebody can chime in with the higth and width of the nylon strip.

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    Thanks for the great pics!

    I can now see why I have binding at the transition area. The outer shell needs bent in and the curve "fixed".

    By the way, the JB Weld build up I tried didn't work out. It kept the rounds from jamming, but the follower binds on the JB Weld and the inner drum won't rotate through that area when transitioning to the next coil.
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    Quote Originally Posted by strobro32
    Looks good!

    Maybe somebody can chime in with the higth and width of the nylon strip.
    And where to get them.
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