twist for saum

Discussion in 'Rifles, Bullets, Barrels & Ballistics' started by vandal, Jun 25, 2011.

  1. vandal

    vandal Well-Known Member

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    I am building a rifle in 7mm saum with a 28'' barrel for long range hunting. What twist for 175 or 180 sierra MK. I am thinking 1:8.5 but I see that 1:9 is popular with folks on the internet. Sierra recommends 1:8. I may entertain using 162 Amax, can the Amax be over twisted with 1:8.5?

    Thanks for the advice
     
  2. J E Custom

    J E Custom Well-Known Member

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    The 1 in 9 is the recommended twist for most 7mm cartriges.

    But with the big bullets in a medium sized case the 1 in 8 to 1 in 8.5 would be best choice
    because of velocity potential of the SAUM.

    If you wanted to use the 162 A Max or the 168 SMK the 1 in 9 would be better IMO.

    J E CUSTOM
     
  3. JeffVN

    JeffVN Well-Known Member

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    Most folks I know using a 7mm are using a 1:9. I use it exclusively in my 7WSM, as does my brother in his .284. Depending upon your chosen season of use a 1:9 will be fine. I have an 1:8.5 that I us for the Matrix 190s, and it shoot the 180 Bergers and 175 Sierra just fine. That having been said I do not hink either one will be a mistake.

    Jeffvn
     
  4. Mikecr

    Mikecr Well-Known Member

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    Even a 200gr Wildcat ULD only needs a 9tw.
    Cartridge don't matter
     
  5. LouBoyd

    LouBoyd Well-Known Member

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    So far no one has mentiond the environment you'll be shooting in. Air density matters in determining the necessary barrel twist. I live at a mile elevation in Arizona where a 9" twist barrel is fine for 180 Bergers. However if you plan on shooting in sub-zero tempeeratures near sea level an 8" twist would be my recommendation.

    In my opinion you need at least a 3.1" magazine for the 7mm SAUM / 180 Berger combination so the bullet shank won't extend inside the case shoulder. The SAAMI cartridge length of the 7mm SAUM is only 2.825" and most short actions don't have close to 3.1" room even with an extended magazine like a Wyatts. I'd use a medium length magnum action (3.34" magazine) if I were building the rifle you've described. You didn't mention what action you plan to use.
     
    Last edited: Jun 26, 2011
  6. vandal

    vandal Well-Known Member

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    Thanks to all for the advice this far.

    I plan to use a stiller predator long action to mitigate any length issues associated with using long bullets. I will be shooting in the 2000-4000' elevation with hunting temps ranging from 30-60 degrees but I will practice all year with temps possible reaching the 90's and down to the 20's.