Looking for a chart...

88fingers

September 19, 2006 14:36

Just starting in on this long range stuff and I am having a blast, although I am doing all of it thru trial and error. I have had a couple of gentlemen giving me advice at the range about bullet weight .vs barrel twist and their effect on accuracy, but information seems to differ from one person to the next. I am looking for some online chart's that show recommended bullet weights for barrel twist rate. I found a few in some old G&A mags that I found stashed around the house, but they don't have all of the info I am wanting. Any web sites would be appreciated.
Thanks folks,


88

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  Tailgunner1954

  September 19, 2006 14:50

  There is a rough guide on the Shilen barrel website.
  I say rough, because what you realy need is bullet LENGTH vs twist rate (and I don't know of anyone that lists it that way).
  
  For long range however, you can use the simple methiod of "the highest BC bullet that will group out of your rifle, is the best one for your long range work". Sierra Matchkings are always a good place to start, with the Nosler BT's running right behind tham (I'm assuming that your not quite ready to move up to the full custom $$$ bullets).

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  sandwarrior

  September 19, 2006 23:48

  88fingers,
  
  There are two formulas that I use when selecting bullets for the rifle I will be shooting with. First is the Greenhill Formula:
  
  Twist = 150 X D2/L
  
  Where:
  D = bullet diameter in inches
  L= bullet length in inches
  150 = a constant
  
  2 is squared not multiply by 2
  
  Substitute 180 for bullets over 2800 fps. muzzle velocity.
  
  Second is the velocity formula:
  
  T=.06 x V x D2/L
  
  Where:
  V= velocity(your intended velocity to start it will narrow down as you chronno
  D= Diameter of the bullet
  L= Length of the bullet.
  
  again, 2 is squared not multiply by 2
  
  Notice nowhere does it give weight of the bullet. It is usually porportionate to the length of a given caliber by a given maker. However, you will find the Berger VLD's require more twist than Sierra Matchkings. Both are very consistent in their specs you will just find a longer ogive on the VLD giving it a higher B.C. The B.C. will come into play at longer ranges. It won't usually matter out to about 300 yds. if velocities are equal. -hope those help.

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