Determining true BC

Discussion in 'The Basics, Starting Out' started by Forester, May 23, 2008.

  1. Forester

    Forester Well-Known Member

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    I have been shooting with good results the Hornady 110gr V-Max through my Savage 12FV this spring and have taken a few groundhogs with it so far. I wanted to work out a real drop chart and get an idea of what kind of groups I might expect beyond the 200 yards I have been working at so far so I took advantage of a nice calm morning today...can some of you that are more experienced at this tell me if my logic is valid here?

    I first made sure I had the rifle well zeroed at 200yards. I checked my 200 yard groups through the Chrono and got the expected 3145fps with very low ES(5-10).

    I then moved out to 400 and used a free ballistics program to get close on how much to come up on the scope. After shooting a 3 shot group I adjusted the scope to zero at 400. I shot a group to confirm and had a good zero at 400 yards.

    I used the actual come up to adjust the BC of the bullet in the program until the programs numbers matched my own.

    I then moved back to 500 and used my new BC in the program to bring the scope up. Hits were exactly at the correct elevation on target.

    Heres what I found hard to believe, if I did things right, my actual BC is .286 instead of the .177 claimed by Hornady. it seems hard to believe that my real BC could be 60% higher than what is claimed by Hornady.

    By the way, groups:

    200= .41MOA
    400= .44MOA
    500= .38MOA

    Groups at 200 are round, at 4 and 500 most of the dispersion is windage, very little elevation.

    Darn good for a (relatively) cheap rifle and Bushnell scope! All I have done is bed the action in the factory stock and open the barrel channel up to make sure it can not touch.

    Thanks for checking my method!
     
  2. jwp475

    jwp475 Well-Known Member

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    What is your elevation? did you correct the BC for elevation?
     

  3. Forester

    Forester Well-Known Member

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    I used 1000 for all calculations...the areas I hunt will run from about 800 to 2500 feet. Mostly closer to 1000-1500

    Not using the exact elevation that I was shooting would mean I have included some of the elevation effect in my real world BC instead of letting the program do things the right way correct?

    If I am figuring things right and the worst case scenario puts me 1000 feet higher in elevation I will be .3 MOA off at 500 yards...for the use this particular load will get I can live with that.
     
  4. jwp475

    jwp475 Well-Known Member

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    Bullet companies BC's are corrected to sea level and the ballistics programs take this into account if memory serves, so if your BC is at altitude then it will have a higher number than one that is corrected to sea level.
     
    Last edited: May 23, 2008
  5. royinidaho

    royinidaho Writers Guild

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    Forester,

    Quit worrying about it and go shoot stuff.:D

    When you have things tuned that close you become one of the few to be envied.;)

    When I input the .7xx for a Sierra 300 gr SMK and input the info for 4500 feet and other conditions the software jumps it to something like .85.

    I don't understand it but the drop chart works.
     
  6. Forester

    Forester Well-Known Member

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    See I have this sickness...I blame my father for it. If there is a higher level of perfection to be attained I can't resist trying for it.

    I don't think many here would envy my shooting...500 yards still seems like a D@%& long ways away to megun)
     
  7. Waltech Jim

    Waltech Jim Writers Guild

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    Forester,

    How happy would you be if Hornady had a BC of .290 for their 308 cal, 110 V-max. (I assume that is the bullet you are talking about.)?

    They obviously just changed it to match your results. Good job.

    Jim
     
  8. Forester

    Forester Well-Known Member

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    light bulbWow, just looked at Hornady's website, I don't know how I got the lower BC number in my head but .290 sure makes more sense.

    Thanks for pointing that out...clearly I'm an idiot:p
     
  9. Ridge Runner

    Ridge Runner Well-Known Member

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    every bullet I ever checked shooting here has a higher actual BC than published with the exception of the lapua 139 gr scenar. I also shoot and hunt from 800-3000 ft.
    the 160 accubonds I shoot alot are published at .531, to get my drops right out to 1k I use .62
    RR
     
  10. KQguy

    KQguy Well-Known Member

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    I am currently shooting the 208gr Amax out of my 300wm,and I have to use .75 bc to get it to match my exbal.I am not sure what there published bc is,but i know it's alot lower than that.