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Thread: Bullet Stabilization

  1. #1
    Join Date
    Apr 2009
    Location
    Paynes Creek Ca.
    Posts
    140

    Bullet Stabilization

    I have been thinking about the stability of the 135 gr .308 SMK in a 17 twist barrel. I called Sierra and the bullet length is 1.085". IIRC another thread sait that a 125 gr bullet at 1.00" length would be stable in an 18 twist barrel.
    I have checked Greenhill with a 1" bullet and a constant of 180 it comes out to 17. So disregarding Greenhill, should a 1.085" .308" bullet be stable in a 17 twist barrel?

    Jeffrey Tooker

  2. #2
    Join Date
    Feb 2003
    Posts
    253
    Quote Originally Posted by Jeffreytooker View Post
    I have been thinking about the stability of the 135 gr .308 SMK in a 17 twist barrel. I called Sierra and the bullet length is 1.085". IIRC another thread sait that a 125 gr bullet at 1.00" length would be stable in an 18 twist barrel.
    I have checked Greenhill with a 1" bullet and a constant of 180 it comes out to 17. So disregarding Greenhill, should a 1.085" .308" bullet be stable in a 17 twist barrel?

    Jeffrey Tooker
    Flat Base bullets, up to 1.100" long work very well via a 1:17" twist - not sure about the BT, but it does reduce drag, thus, Sg - I'm guessing that at least during spring, summer, and fall temps, they'll work well enough. To get a better idea, go here - http://www.eskimo.com/~jbm/cgi-bin/jbmdrag-5.0.cgi - enter the data (measurements) you get from the bullet in question and you'll get close approximation of Sg via a 1:17" twist, and the twist recommendation to achieve SG of 1.5. RG

  3. #3
    Join Date
    Feb 2003
    Location
    AUSTRALIA
    Posts
    169
    In my area the 135 is good to go in an 18 twist,shoot good for a factory bullet too even as the range extends past 200..JR..Jeff Rogers

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