A ballistic coefficient (BC) is a numerical description of a projectile's aerodynamics. Shooters are concerned with this value because it describes the rate at which a projectile decelerates. The higher the value, the slower the bullet decelerates. The BC and muzzle velocity determine the bullets trajectory.
Many software packages are now available to calculate downrange trajectories. For example, Sierra Infinity Ballistics Software provides this feature as well as the many equations used in the calculations.
Energy is the measure of the work performed by a bullet, typically expressed in foot pounds. This figure is calculated by the following equation:
W = bullet weight in grains
V = velocity in fps
((W)(V squared)) divided by 450, 240