BC = (R1 – R0) / (log(V0/V1) * 8000)
Where:
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)
Where:
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.
