G function question

Discussion in 'Rifles, Bullets, Barrels & Ballistics' started by trader388, Oct 11, 2004.

  1. trader388

    trader388 Well-Known Member

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    Feb 12, 2004
    two bullets: berger 7mm 180gr VLD, berger 30cal 210gr VLD.
    two trajectories:

    1. mv3000, BC .698, weight 180gr, zero 200yrds, max range 2000yrds, increment 100yards, humidity 75%, altitude 1000. All otheres default.

    2. mv3000, BC .640, weight 210gr, zero 200yards, max range 2000, increment 100yrds, humidity 75%, alt 1000. All others default.


    trajectory 1 using default G function (g1) - @2000 yards: drop = -1680, windage =274.5

    trajectory 2 using default G function (g1) - @2000 yards: drop = -1851.3, windage = 308.5

    trajectory 1 using G 7 function - @ 2000 yards: drop = -1009, windage = 105.3

    trajectory 2 using G7 function - @ 2000 yards drop = -1051, windage = 117.9

    Which is right? Note: I've used 2000 yards because it shows the greatest difference for ease of learning purposes.

    Also...

    Is the 240gr. sierra match king considered a VLD...what g function to use?
    Is the 300gr. sierra match king considered a VLD ...what g function to use?
     
  2. Richard338

    Richard338 Well-Known Member

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    Aug 22, 2003
    The published BCs that you enter are G1. The G7 (or other) might be more appropriate for a particular bullet. If you want to use G7, you must convert your BC. You can't use the G1 BC. People like to quote the G1, since it tends to be the largest.
     
  3. trader388

    trader388 Well-Known Member

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    Feb 12, 2004
    sovles that. Thanks. [​IMG]
     
  4. Jeff In TX

    Jeff In TX Well-Known Member

    Messages:
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    Joined:
    Aug 10, 2003
    Trader 388,

    Sierra matchkings are truly boattail bullets and not VLD. They would use a G5 drag model, which was developed for boattails and not the G7, which was developed for VLD bullets.

    I used my RSI ballistic program, which will convert bullet drag functions. I can also take the bullets dimensions and plug them into a drag model estimator, which will tell you what drag model is correct. The sierra boattails definitely fall under the G5 drag model.

    Below is the G5 BC for the bullets your were asking about.

    240gr. sierra match king G1 BC is .711 converted to G5 is .411

    300gr. sierra match king G1 BC is 768 coverted to G5 is .477

    Hope it helps