barrell twist rate?

one2hutn

February 07, 2009 13:27

Where can I find info on how twist rate correlates to optimum bullet size?
Thanks,
Chris

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  FEENIX

  February 07, 2009 19:21

  Not really sure what you're looking for but try these ...
  
  http://kwk.us/twist.html
  
  http://www.z-hat.com/twistrate.htm
  
  http://www.realguns.com/calc/riflingtwist

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  sandwarrior

  February 08, 2009 05:25

  One2hutn,
  
  I don't know where it's published but nn gave me this formula some time ago. It's a modification of the Greenhill Formula for twist.
  
  V x .06 x D(sq.)/L
  
  V= velocity
  D=diameter
  (sq)=squared
  L=length
  
  Note in there that weight isn't directly factored in. If all bullets were one standard shape and construction it wouldn't matter, you would use weight. But this formula works on length not a weight conversion factor.
  
  The original greenhill forumla is: 150 x D(sq)/L. That ended up being modified for fast moving bullets (above 2800) to: 180 x D(sq)/L
  
  These are just guidelines for what twist will and won't work. I have a 1-10" 6mm-.284 that will stabilize 105 Bergers but won't stabilize 95 gr. Sierra Match bullets. I'm thinking it has more to do with how the weight is distributed over the length of the bullet. Sometimes you just have to try a bullet out to see if it will stabilize...within reason. I tried some 142 Wildcat's in my 1-10" .25 cal's...they won't stabiize.
  
  Anyhow, try the links FEENIX gave you too. Always good information to test out.

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  one2hutn

  February 08, 2009 06:34

  Thanks again!

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