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Math behind Elevation Adjustments

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Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: May/26/2011 at 21:30
08Cayenne View Drop Down
Optics GrassHopper
Optics GrassHopper


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I was interested in the math used to calculate elevation adjustments for different yardages.  I know you can buy software to do this but I would like to understand the math before I buy.  My novice guess would be you need bullet weight, muzzle velocity, bullet drop, maybe wind speed and direction, temperature, humidity....  Any info would be appreciated.
 
Thanks
Frank
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: May/26/2011 at 21:34
supertool73 View Drop Down
Optics Jedi Master
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Superstool

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There are a lot of free online ballistic calculators.  JBM is one of them.  http://www.jbmballistics.com/index.shtml  That site has a ton of info and could probably answer all your questions.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: May/26/2011 at 21:51
08Cayenne View Drop Down
Optics GrassHopper
Optics GrassHopper


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Thank You Sir, looks like exactly what I'm looking for.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: May/27/2011 at 14:30
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Optics Master Extraordinaire
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Here's a couple tips on using JBM or other ballistics calculators:

  1. Aside from bullet weight, which obviously easy, you also need to know the ballistic coefficient (BC). This you can get from the manufacturer's website, although be aware that some BCs are on the optimistic side.
  2. You need to know which drag model is used with the BC. Most often it is G1. But some brands like Berger, provide G7 and G1 BCs. The G7 model is more appropriate for boat tail bullets. But out to 600 yards or so it doesn't matter much. The important thing is make sure you know which drag model was used.
  3. Muzzle velocity is best determined with a chronograph but if you don't have access to one and are using commercial ammo you could ballpark it with a published figure.
  4. The most important exterior variable is atmospheric pressure because this affects drag the most. JBM can be confusing until you know the difference between standard and corrected pressure. If using corrected pressure (like you get in a weather report or from the nearest airport, e.g. 30.02) you need to enter the altitude and indicate that the pressure is corrected. With a standard (uncorrected) pressure, e.g. 24.84, you enter 0 as the altitude.
  5. Next most important is temperature. Try to be accurate on this.
  6. Humidity has little effect. Don't worry if you don't have it. Contrary to what you might think, the higher the humidity, the less the drag.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: May/27/2011 at 15:20
Shenko View Drop Down
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exteriorballistics.com is Sierra Bullets' site.
There's enough information there to keep a guy busy for a while.
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