Chrono vs. Range Dope HELP

Discussion in 'Long Range Hunting & Shooting' started by Magnum61, Aug 31, 2011.

  1. Magnum61

    Magnum61 Well-Known Member

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    I have one of these...

    Competition Electronics ProChrono Digital Chronograph - MidwayUSA

    It says that my 210 Bergers out of my 300 win mag are going 2865 fps. But if I leave the BC alone in the calculator and change the velocity to match range dope, it matches 2805-2810 fps.

    I have other field data that the 2810~ matches on gong shooting but while the 875yd data and closer matches... the 1000yd data in .8 MOA less than what the Calculator is putting out.

    Any thoughts?
     
  2. budlight

    budlight Well-Known Member

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    bullets don't have a static BC. Some manufactures give the change in BC within velocity ranges. Example is a .560 BC at 2800 + FPS At 2400 FPS the BC is only .530 and at 2000 fps it is now only .500.


    So for a long shot you have to get an average BC because of the decreasing BC

    I think Sierra bullets lists velocity changes BC's for their bullets.


    I've often wondered about aerodynamic changes with a 6 groove barrel over a 3 groove. That is why range BC calculating with real life bullet drop actually shows true projectile BC. Some manufactures list highly overrated BC's for their VLD bullets just to make a sale and the bullets never live up to advertised BC in the field
     

  3. J E Custom

    J E Custom Well-Known Member

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    Very well said !!!!

    Both the chronograph and actual drop tables are tools to calculate "TRUE" BCs of a bullet.

    J E CUSTOM
     
  4. Catfish

    Catfish Well-Known Member

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    If the center of the scope heitgh over the center of the bore has an effect on the drop chart, or a BC ratical. You should field check your drop chart befor you go to the field hunting.
     
  5. Magnum61

    Magnum61 Well-Known Member

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    So here is My load:

    300 win mag
    Nosler Brass
    75.5gr of H1000
    TOUCHING LANDS
    FED 215M Primer
    210 Berger HUNTING VLD

    GUN:

    R700
    26" Lilja 3-Groove 1/11" 30cal, #4 Heavy Flutes
    HS Precision Stock
     
  6. Broz

    Broz Well-Known Member

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    Magnum61, I do a lot of work with 300 Win's, 210 Bergers and H-1000 using the old .631 BC as well a the new .616. Just looking at your load and barrel length, If I had to guess I would say your MV should fall into the 2840 to 2860 range. So you might wish to look at second chrono's info. Or simply work it out to your actual field tested drops and don't worry about what the number are. After all they are just numbers. Spot on drops are real and what we seek.

    Jeff
     
  7. Magnum61

    Magnum61 Well-Known Member

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    I've been using the G7 instead of the G1. Will that make a huge difference?
     
  8. Broz

    Broz Well-Known Member

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    No, you are fine with either, and the G7 will help out past 1200 to 1400 and beyond. But I feel with this caliber either should work out good.

    Jeff
     
  9. WildRose

    WildRose Well-Known Member

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    Yep... .