338 Super

Discussion in 'Gunsmithing' started by J E Custom, Dec 10, 2011.

  1. J E Custom

    J E Custom Well-Known Member

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    I have been a fan of the RUM s for quite a while and have been playing with a "Improved"
    version (That remains to be seen until all testing and evaluating is done) of the 338/375 Rum.

    There have been several people instrumental in helping me coming up with this cartrige so
    I dont want to take full credit.

    I call it the super because it is all you can do to a 375 RUM case that is practical, moral and
    usable to increase powder capacity.

    At this writing hear are some of the results and features.

    Case capacity (Water) before Final fire forming 115. grains.

    Case capacity (Water) 122.3 to 122.5 AVG 122.4. after fire forming.

    Case capacity (Retumbo) 118.4 as pored (No drop tube).

    Accuracy was very good during break in= 5 shot .381 and after break in= .171 @ 100 yards.
    these loads were fire forming and break in loads using the 200 gr Accubond and re 25
    (Undisclosed amount) without a chronograph.

    Load development will now begin and a chronograph will be used, and will be shot @
    extended ranges (200 to 600 yards).

    The test rifle is built on a Weatherby Mark 5 action And has a 31" barrel with a Ross Schuler
    break.

    After more testing I will post the reamer spec. and the brass forming procedure plus the loads
    and performance of the round.

    I will also post my opinion if it was worth the effort to wild cat the RUM case to this extent
    for the amount of improvements in Velocity.

    My intent is not to push the cartrige Hard just to see what I can get from SAMMI pressures
    and extend the brass life.

    I should have the final results within a month (With Christmas and Hunting season being the
    reason for the delay).

    Even if it does not work out to be practical it has been interesting and a learning experance.

    J E CUSTOM
     
    Last edited: Dec 10, 2011
  2. winmag

    winmag Well-Known Member

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    Sounds like a pretty awesome idea! Keep us posted
     

  3. HARPERC

    HARPERC Well-Known Member

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    Sounds interesting.
     
  4. TikkaShooters

    TikkaShooters Official LRH Sponsor

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    Definitely keep us posted.
     
  5. Akiona

    Akiona Well-Known Member

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    :rolleyes::rolleyes::Dgun)
     
  6. CA48

    CA48 Well-Known Member

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    What are your velocity expectations with the 300 gr. bullets.
     
  7. geargrinder

    geargrinder Well-Known Member

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    338 Edge Improved?
     
  8. J E Custom

    J E Custom Well-Known Member

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    I am hoping to break the 3000 ft/sec mark without excessive pressure but 2900+ will be ok
    as long as pressures are reasonable.

    That does not sound like much but even a 50 ft/sec increase for the 300gr bullet is significant.

    Hopefully the extra capacity will allow me to use more slower burning powder and hopefully
    the 31" barrel will consume it.

    To soon to know but time will tell.

    J E CUSTOM
     
  9. bassin93

    bassin93 Well-Known Member

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    I guess I always assumed the 375 rum was a 300 rum necked up and have never looked at the specs. Is this not the case......we could really have a SUPER?
     
  10. J E Custom

    J E Custom Well-Known Member

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    Sorry ; I did not see your post.

    No; it is larger and has more capacity.

    It has a longer case body, less taper per inch (.010 thousandths end to end)and a shorter neck
    than the Edge Improved.

    It does have the 40o shoulder and will hold 6 to 7 grains more powder than the Edge Improved.

    The 378 Weatherby case will still hold more powder than the super but hopefully it will match
    the 338/378 and with a standard magnum bolt face and 1/3 rd the cost for brass it will be worth
    the trouble.

    I have always been happy with the 338 RUM except when it comes to using bullets larger than
    250 grain.

    J E CUSTOM
     
  11. bassin93

    bassin93 Well-Known Member

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    Please keep us posted on this one, very interesting
     
  12. J E Custom

    J E Custom Well-Known Member

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    Y'all type faster than I do, so I will wait for more questions and try to answer them together.

    And yes the 375 RUM case is almost the same. But the reason for using it is to be able to
    neck it down to finished neck length and leave a "Donut" to head space the longer case
    for fire forming and I can turn the necks before sizing down and keep neck wall thickness
    .014+ without the thinning of the neck when sized up.

    There is a method to my madness.

    J E CUSTOM
     
  13. sp6x6

    sp6x6 Well-Known Member

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    Glad your keeping busy in the off season. Sounds like you have your magnum moose killer, love those big 338'sgun)
     
  14. CA48

    CA48 Well-Known Member

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    3000 fps without excessive pressure would be quite an
    accomplishment with the RUM case.

    Hope everything works out, if so I know what I'm rechambering
    to next.