I need some help understanding why the formula to calculate the BC of a projectile is what it is.
In Bryan Litz’s AB for LR Shooting (3rd Ed), he writes:
BC = (projectile weight) / (cal^2 * i)
Where “i” is the form factor of the projectile’s drag coefficient as it compares to the standard G1 drag curve.
I’m confused because as most HPBT/VLD projectiles have *lower* drag coefficients than the standard G1 projectile, they have large form factor values at supersonic velocity.
However, if you increase “i” (form factor) in the BC equation, it reduces the calculated BC value. I understand the basic algebra at work, but I don’t understand the aerodynamic principles that the BC equation is derived from.
If a projectile has a very low drag coefficient, it would have a large form factor, and I would think it should have a very high BC. The equation shows the opposite to be true.
Why is this the case?
Edit: Answered my own question! The standard G1 (or G7, for that matter) is multiplied by the form factor. The form factor is not subtracted from the standard curve values. Therefore, a small form factor would indicate a very low drag coefficient..then, when that small form factor is plugged into the BC equation, it increases the calculated BC value. Thanks for coming to my Ted Talk.
In Bryan Litz’s AB for LR Shooting (3rd Ed), he writes:
BC = (projectile weight) / (cal^2 * i)
Where “i” is the form factor of the projectile’s drag coefficient as it compares to the standard G1 drag curve.
I’m confused because as most HPBT/VLD projectiles have *lower* drag coefficients than the standard G1 projectile, they have large form factor values at supersonic velocity.
However, if you increase “i” (form factor) in the BC equation, it reduces the calculated BC value. I understand the basic algebra at work, but I don’t understand the aerodynamic principles that the BC equation is derived from.
If a projectile has a very low drag coefficient, it would have a large form factor, and I would think it should have a very high BC. The equation shows the opposite to be true.
Why is this the case?
Edit: Answered my own question! The standard G1 (or G7, for that matter) is multiplied by the form factor. The form factor is not subtracted from the standard curve values. Therefore, a small form factor would indicate a very low drag coefficient..then, when that small form factor is plugged into the BC equation, it increases the calculated BC value. Thanks for coming to my Ted Talk.
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