Helpin me understand BC's

Discussion in 'Long Range Hunting & Shooting' started by 460or338, Feb 17, 2010.

  1. 460or338

    460or338 Well-Known Member

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    bc are measure from .000-1 ?closer to 1 the better the bullet retain energy etc.Most ballistic C/ i have seen is .900+ which was a .510 caliber.Does caliber have a affect on the coeffient?. does a longer bullet have a better coeffient?. does a flat point or blunt point have a lower bc?
     
  2. RockyMtnMT

    RockyMtnMT Official LRH Sponsor

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    In general terms the answer to your questions is, yes. We have had some great bc discussions in the last month that would be worth looking up. I believe the actual formula that makes up bc was posted by Bryan from Berger. The shape of a bullet and it's mass play the biggest role in a particular bullets bc. It is all things combined. The very high bc bullets tend to be longer and require a faster twist to stabilize them. There are some very high bc bullets on the verge of coming available, but conventional twist rates will probably not be able to shoot them.

    If you look back in the bullets, barrels, and ballistics, you will find the bc discussions that took place recently.

    Steve
     
  3. J E Custom

    J E Custom Well-Known Member

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    BCs are calculated by two methods.

    The G1 method is based on a comparison of the bullet your trying to measure and a standard
    bullet shape that is a flat base spitzer. This is the method used by most because it has been around for a long time and the BC number is higher.

    The G7 method is the most accurate comparison because it compairs your bullet to a model
    shaped more like the new technology bullets we have today (Boat tailed spitzer). The reason
    manufacturers don't use it is the numbers go way down,and as you know numbers sell bullets.
    It is the same bullet but different numbers. The main advantage to the G7 Ballistic coefficient
    is that if you test the bullet at range the drop and drift figures are a closer match (More
    accurate numbers).

    The measurement for BCs can start very low .100 to .200 for round ball to well over 1.000
    The .510 BCs using the G1 method are as high as 1.124 but when you use the G7 method
    it drops to less than .600.

    All of the highest bullet BCs are on the secant ogive or the tangent ogive with boat tails because
    they are longer and more aerodynamic that the other shapes of the same weight.

    Round nose and flat nose bullets have a poor SD because of there shape and most are flat base
    and are much shorter for there weight.

    Ballistic Coefficients are not as important for some uses as it is for long range and in fact high
    BC bullets are not as good as round/flat nose designe,s for thick skinned dangerous game.

    To help explain what the shape of a bullet has to do with BCs (the ability to move through the
    air ) I would use a simple comparison A sail boat or a tug boat . The sail boat is designed to
    move through the water with the least amount of effort, But the tug boat has a different
    design criteria and speed and ease through the water is not important.

    I am a layman and not a ballistician so hope I have helped explain what BCs are and
    the number system used.

    J E CUSTOM
     
    Last edited: Feb 19, 2010