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Jeffreytooker
05-28-2009, 03:58 PM
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

R. G. Robinett
05-28-2009, 04:24 PM
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

a.JR
05-28-2009, 05:24 PM
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