Twist rate for 7WSM...

Discussion in 'Rifles, Bullets, Barrels & Ballistics' started by MikeW, Jan 4, 2002.

  1. MikeW

    MikeW Well-Known Member

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    May 28, 2001
    I'm building a 7WSM and plan on shooting the
    162 AMAX,162&168 grain Berger VLD's.
    What twist rate would you recommend?

    TIA
     
  2. Boyd Heaton

    Boyd Heaton Well-Known Member

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    May 14, 2001
    I am having a 7mm Rum built.I too will shoot 162's.I told the people building it what bullet I wanted to shoot and they used an 8 twist.
     

  3. Warren Jensen

    Warren Jensen Well-Known Member

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    May 3, 2001
    Having a barrel cut with a specific twist for a specific bullet is a science. If you want a barrel that will shoot more than one bullet and bullet weight then you have to compromise.

    My general recommendations for the two cartridges mentioned are: 1:12 is too slow, 1:8 is too fast. 1:9 or 1:9.5 is about right, unless you will use mainly lighter bullets, then 1:10. Remember, a bullet is at it's most accurate when it is "just stable" at the muzzle. This is usually considered to be a Stability Factor (SF) of 1.3-1.5.

    A 1:8 would be appropriate for an extremely optimized and heavy VLD. A 1:12 won't stabilize some heavier 7mm bullets at moderate velocities.
     
  4. Varmint Hunter

    Varmint Hunter Well-Known Member

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    The Hornady 162gr A-Max is a very long bullet for its weight and diameter. As such, you will need a 9 twist or faster to stabilize it. According to Hornady, my 10 twist Hart barrel (7STW) will only keep this bullet stable for about 100yds before it becomes UNstable in flight.
    I'd opt for the 9 twist which should be capable of handling most bullets up to 175gr. An 8 twist barrel may be good for a particularly long and heavy, special purpose bullet but I really don't see the practical use of it. [​IMG]
     
  5. MikeW

    MikeW Well-Known Member

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    May 28, 2001
    Thx. Guys.
    This gun is for 1000 yrd IBS competetion
    and long range Prairie dogs and coyotes.

    I don't plan on doing any deer or big game hunting with it. That's the reason for just match bullets with a high BC.

    I'm not really concerend with shooting any of
    the lighter hunting bullets although it might
    be fun to see just how fast I could push a
    100 grian HP out of it.