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Old March 14, 2000, 11:57 PM   #2
Bud Helms
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Join Date: December 31, 1999
Location: Middle Georgia
Posts: 13,003
BC = w/i(d*2)

BC = weight of the bullet divided by the product of the diameter of the bullet squared and the coefficient of form

i = ? Ah, now we get to it. Coefficient of form is usually given. Hell, BC is usually given.

There is a chart which was published by E.I.Du Pont De Nemours & Co., which was prepared by Wallace H. Coxe and Edgar Beugless, Ballistics Engineers (and principal investigators) of the Smokeless Powder Dept at DuPont's Burnside Laboratory in Wilmington, Delaware, in 1936. Actually it is one in a group of ten charts that were part of an extensive publication on ballistics.

Chart No. 1 is for determining Coefficient of Bullet Form. Chart No 2 is for determining Ballistic Coefficient. And so on.

Without the chart, I don't know how to do it. It is an estimate even with the chart. The ogive of the bullet is determined by comparison with a set of drawn examples which are numbered. That value is taken to a table and a selection is made which yields another value. That number is Coefficient of Form (i). There is not enough information in the table to empirically derive a relationship which can be expressed mathematically.

So, the BC in the reloading manual is usually taken as the truth because computing it is a pain in the arse! I came into the charts when I purchased P.O. Ackley's Handbook for Shooters and Reloaders, Vol. I and II.

Reloading books published by bullet mfgs always (these days) include the BC for every bullet listed. Not so in reloading books by powder mfgs. They treat the bullet as a mass with inertia and assume nominal values. That's not incorrect, it's just incomplete.

As I understand it, Coxe and Beugless based some of their work on results of testing and earlier ballistics-related computations taken from Krupp Industries in Deutschland. Krupp was the foremost military and heavy weapon maker of the 19th and early 20th Centuries.

[This message has been edited by sensop (edited March 15, 2000).]
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