The ballistic coefficient (BC) of a bullet is a measure of its ability to overcome air resistance in flight. The factors that influence a bullet's BC are the bullet's mass, diameter, sectional density, and and shape. Bullet's with high ballistic coefficients are more efficient in the air and retain their speed better than bullets that have lower ballistic coefficients. You may find the ballistic coeffecient of a projectile by looking on the product packaging, the manufacturer's website, or by searching the internet.