0.264 13.843 0.338 22.691 0.277 15.24 0.358 25.456
For the marketing of the formulas, they were brilliantly
laid down on a slide rule type of device so we didn’t have to go through the longhand set of formulas. Alas, today the slide rule is long out of production. But all is not lost. For those who are energetic and have a simple en-
gineering or scientific hand-held calculator, the original longhand formulas are available in print, in a book pub- lished by the NRA titled “Handloading,” by Wm. C. Davis Jr. Bill and Homer were great friends and worked together for the Department of Defense for many years. In his book, he praises the formulas, and goes into great detail on how to use them. “Powley’s equations are remarkably accurate when calculating starting loads, considering the complexity of internal ballistics,” Davis wrote. For those not so energetic, and with a few extra dollars
and with a computer, Wayne Blackwell’s “Load From A Disk” computer program incorporates the Powley Formu- las. The imput data for the computer program is exactly the same as it is for the original Powley Computer slide rule. (The program was also reviewed in The VARMINT HUNTER Magazine®, in October 2000.) And for those who will settle on just knowing the
optimum DuPont powder and its starting charge for the cartridge in question, there is a quick fix/short formula we can play with: 20 + (12 divided by the sectional density of the bullet times the square root of the optimum powder charge divided by the bullet weight). The optimum powder charge is 86% of the water
weight, to the base of the bullet (should the calculations below determine that IMR 4227 and IMR 4198 are our opti- mal powders, then we must use 80% for a starting charge). The sectional density is listed in all bullet manuals, along with the ballistic coefficient of the bullet. And this formula will give us a number known as “the Relative Quickness” of the powder we should be using. Below is a paragraph detailing the DuPont powders, with their corresponding relative quickness numbers. Powder/Relative Quickness: IMR-4227/180, IMR-
4198/160, IMR-3031/135, IMR-4064/120, IMR-4895/115, IMR-4320/110, IMR-4350/100, and IMR-4831/95. In closing, let me note that we handloaders are too
spoiled. Loading manuals abound, and gun magazines seem to have covered, ad nausea, loading data for every comceivable factory and wildcat round. But for a wildcatter starting from scratch, there’s no tool available that’s more valuable than Homer’s equations.
Author’s Note of Caution:
As stated above, these formulas are meant only for high- intensity cartridges to be used in modern bolt-action and single-shot rifles (like the Ruger No. 1). Under no circumstances should they be used to generate loading data for old black powder cartridges in lever guns and single-shot rifles like the .45-70 Government and so on.
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