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.
