2.3 How the Ballistic Coefficient is Measured

We first began to investigate just how to determine the BC values of various bullets in 1969. We learned very quickly that BC values for all bullets need to be measured by firing tests; there is no other way to make an accurate determination. It is true that in 1936, E. I. Du Pont de Nemours & Company, Inc., published a brochure prepared by two ballistics engineers on their staff, Wallace H. Coxe and Edgar Beugless. This brochure, titled Exterior Ballistics Charts, described a method of finding the form factor of a bullet by matching the point shape against a set of ogive contours, and then looking up the form factor value in a table of values. With the form factor known, the BC could then be obtained from a chart in the brochure. The brochure also contained several pages of nomographs and simple computational techniques to determine trajectory variables, such as remaining velocity, maximum trajectory height, wind deflection, etc., versus range from the muzzle.

The work of Coxe and Beugless was a great step forward at the time. They presented the first method of BC estimation available to the general shooting community, and their nomographs presented a useful method of calculating ballistics parameters long before the age of computers. Their methods were used by handload developers and wildcatters until several years after the end of World War II. Today, however, the work of Coxe and Beugless is mainly of historical interest. We found in 1969 and 1970 that BC values determined by their method simply are not accurate enough by modern standards. BC values really must be measured by firing tests. We have used three methods of measuring BC values from firing tests. The first two of these methods can be used by shooters equipped with a pair of chronographs, a computer, and exterior ballistics software such as the Sierra Infinity program.