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Old 6th October 2013, 01:25 PM
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rich rich is offline
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Location: Shebbear, N Devon
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BC = (R1 – R0) / (log(V0/V1) * 8000)


BC = Ballistic Coefficient
R0 = Starting Range (where V0 is measured) [Yard]
R1 = End Range (where V1 is measured) [Yard]
V0 = Velocity at R0 [Ft/s]
V1 = Velocity at R1 [Ft/s]

You’ll need two chronographs. If one is measuring muzzle velocity (and is therefore close to the muzzle) then the expression becomes:

BC = R / (log(MV/V1) * 8000)


BC = Ballistic Coefficient
R = Range between the chronographs [Yard]
MV = Muzzle Velocity [Ft/s]

Note that the expression is extremely sensitive to the accuracy of the velocity measurements; less so to the range estimation.

8000 appears to be a rather arbitrary constant.
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