Shimming an M39
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Thread: Shimming an M39

  1. #1
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    Default Shimming an M39

    How do you know when to shim or not shim an M39? How do you know how much to shim?
    Looking for USS Casimir Pulaski SSBN 633 items.

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  2. #2
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    Quote Originally Posted by VA-Vet View Post
    How do you know when to shim or not shim an M39? How do you know how much to shim?
    VA-Vet, In general, shims are used to correct misalignment or interference between the stock and the barrelled action.

    I shim to free float the barrel in the stock with the action bolts tight and the gun in the shooting hold.

    Start by removing the front hand guard and examine any pressure or gap between the barrel and the barrel contact point at the tip of the fore stock.

    Daniel39

  3. #3
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    Wait for Leon to chime in on this one. He tutored me with mine and can explain it quite well.
    The blood runs free, the rain turns red, give me the wine, you keep the bread.

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  5. #4
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    Start with a few slow fire bench test targets at 50 and 100 yards as a base before making any changes, using top quality ammo. Clean cold barrel. Use very small targets, maybe just black circles on bright white.

    Shimming is done to correct problems or to stabilize bedding. You may not need it, but you need a test basis to find out and to see if any changes actually improve anything.

  6. #5
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    Once you figure out what shimming is correct then you can play with the tension of the nose cap screw as that will also make a difference in your accuracy.
    The blood runs free, the rain turns red, give me the wine, you keep the bread.

  7. #6
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    Default Procedure for Checking The Bedding of the Finnish M39

    Quote Originally Posted by Heavy Metal 1 View Post
    Wait for Leon to chime in on this one. He tutored me with mine and can explain it quite well.
    (Mods: I have answered this question numerous times over the years, and have asked repeatedly that my procedure be made a sticky. It has not. So kindly do me the same courtesy I am providing this forum member, and make this a sticky.) Remove the action screws, barrel bands and handguard. Place the stock with the barreled action in a vise or other fixture. With your thumb press down on the tang of the receiver. The action should rock slightly - longitudinally - and the barrel should rise about half its thickness above the stock at its end. If this is so, reinstall the action screws, tang screw first, then magazine action screw, and verify the barrel is free floating by passing a piece of paper between the stock and barrel along its entire length.(Paragraph break.) If the action does not rock slightly, as described above, shimming is needed. This is located on top of the area inside the stock directly behind the action lug recess. Add shim stock until the action rocks slightly when pressing down on the tang. (Paragraph break.) The action screw tightening sequence is as follows. Start both action screws. Tighten the tang (rear) action screw and observe how the barrel rises up out of the stock channel. Stop tightening when resistance is first felt. Now tighten the magazine - front - action screw and observe that the barrel settles back into the stock channel. Tighten the tang - rear - action screw completely. Then tighten the magazine - front - action screw completely. (Paragraph break.) The action screw tightening sequence, in conjunction with the the receiver shim, places the birch stock under tension and thereby it acts as a damper spring. This is analogous to the way the Swiss K31 action is bedded, with the tension provided by the curvature of the trigger guard.

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