BC (Ballistic Coefficient)
In simple terms, BC is a measure of how well a bullet resists air drag, and thus, retains its velocity as it travels through the air. The higher the number, the more velocity a bullet retains at a given range. Ballistic coefficients range in value from 0.08 to 0.7 for typical sporting bullets.
The ballistic coefficient of a bullet tells how well it resists air drag compared with a standard bullet. If a particular bullet resists air drag as well as the standard bullet, then it has a coefficient of 1, but if it resists air drag only half as well as the standard bullet, then it has a coefficient of 0.5. Published ballistic coefficients of all sporting bullets (that we know of) are calculated using the G1 projectile and assume standard sea level atmospheric conditions. For this reason, ballistic coefficients calculated by the program are corrected to sea level conditions. Likewise, all ballistic coefficients you enter into the program should also be for sea level conditions.