300WM to 300RUM?

Discussion in 'Gunsmithing' started by moosehunter, May 31, 2010.

  1. moosehunter

    moosehunter Well-Known Member

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    Is it possible to rebarrel a win mod 70 in 300WM and open the bolt face and chamber to 300RUM?
     
  2. kiwi3006

    kiwi3006 Well-Known Member

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    300WM and 300 RUM use the same bolt face. You might need to open the feeding lips on the magazine as the RUM is a fatter case, but you might get away with it.
    Otherwise the rebarrel should not be a problem.

    Stu.
     

  3. J E Custom

    J E Custom Well-Known Member

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    Yes. The bolt face will work for both. (Rim dia. win mag =.532) and the RUM is .534.

    The OD of the belt is .513 and the base of the RUM is .550 So you can re barrel or
    just re chamber if you have a good barrel.

    The action rails may have to be opened up a little to except the larger case of the RUM.

    Also case length is .330 thousandths longer on the RUM but should work as long as you
    have a magnum action. Note some of the Winchesters have a 3006 length action (Long
    but not as long as a magnum action) so check to see if you will have enough length before
    you break it down or re chamber it.

    I hope this helps.

    J E CUSTOM
     
  4. phorwath

    phorwath Well-Known Member

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    JE,
    When rechambering from 300 WM to 300 RUM, does the chamber reamer run in concentrically to the bore before the pilot reaches the lands? Do you end up with a concentric chamber while the chamber reamer pilot isn't engaged in the bore due to the smaller 300 Win Mag chamber preventing the 300 RUM chamber reamer pilot from reaching the bore?
     
  5. J E Custom

    J E Custom Well-Known Member

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    Reamers have a tendency to run centered even if the pilot does not touch if you go slow.

    I was worried the first couple of times doing this but the chambers were as perfect as the chambers that were cut from scratch.

    In the case of 300 Win to 300 rum the pilot will reach long before the chamber is finished
    and if the reamer is set up correctly will end up perfect.

    My preference is to set the shoulder back the length of the tenon and start there, but if the
    barrel is already short you may loose 3/4'' and reduce velocity to much for your needs.

    J E CUSTOM
     
  6. phorwath

    phorwath Well-Known Member

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    Thanks for your response. I've always had that underlying concern with rechambering, and never knew if it was justified or not.