Originally Posted by Browninglover1
I'm not being a jerk when I ask this, but do you have an article I could read that talks about how BC's are computed? I remember reading an article in Shooting Times many years ago that said BC's are calculated off of the G1 drag model that only takes into account a bullets shape. The problem with the low drag bullets is that they are so far removed from the standard G1 model that results can be drastically different depending on what velocity you are shooting the bullets at. That is supposedly the reason that the G7 standard was developed because it computes a number based of a model that much closer resembles the actual low drag bullets.
Again, I don't want to sound like a jerk but I would really like to understand. Like I said, I understood that BC's were computed off the "drag factor" determined by bullet shape and had nothing to do with weight, but I could definitely be wrong.
BC's are calculated in different ways.
Hornady's 8th edition reloading manual has a couple of chapters that explain in some detail ballistics including how BC's are computed.
There are two basic ways.
Once is Drag of a standard projectile divided by drag of test projectile.
The other is more complex where you have:
BC= WID2 (D squared) where
W=mass in lbs.
I=coefficent of form factor
D=Bullet Diameter (measured in inches).
In short both methods tell you how efficiently a bullet will fly at a given velocity.
BC's are not however static as they change as velocity changes.
Bullets that fly the most efficiently at high velocity tend to destabilize when transitioning from Supersonic to Subsonic speeds.
Bullets designed for subsonic stability will not fly well at all at supersonic velocities.
Think about a Piper Cub and the SR-71. The cub flies great and is extremely manueverable at low speeds, but would tear itself apart if you you pushed it beyond Mach 1.
The SR71 flies at Mach2 plus extremely efficiently but cannot fly at all at low speed.
Calculated BC's are very helpful in picking bullets, but the highest BC will not always be the best bullet for every application.