The Ballistic Coefficient http://www.hornady.com/ballistics-resource/external
Before discussing this topic in more detail, let's dispel some myths surrounding it. Whatever you may have heard before, these are the facts:
* There is no such thing as an absolute and invariable ballistic coefficient (B. C.)
*Ballistic coefficients are only one factor in bullet selection for different kinds of shooting.
*A ballistic coefficient can change with reference to (1) altitude, (2) temperature, (3) atmospheric pressure, and (4) relative humidity.
*Ballistic coefficients are measures of a bullet's relative efficiency.
*Ballistic coefficients are not measures of a bullet's "goodness."
*Higher B.C.s do not necessarily make a bullet "better."
* Lower B.C.s do not necessarily make a bullet "worse."