jwl3715,
Homer Powley was a ballistician, chemist, and author who’s career spanned the 1940’s thru 1970’s working in industry and for the military. He was the contemporary of men like Julian Hatcher, Ken Waters, and Elmer Keith. While writing for Handloader magazine in the 1960‘s, Powley developed a mathematical technique for selecting which type of smokeless powder was most appropriate for any particular cartridge and bullet combination. It also estimated muzzle velocity and pressure in cup.
He marketed his technique, in the days before home computers and calculators with nine decimal places, by way of a cardboard slide-rule device called a “Powley Computer”. The screen shot you see is a version I wrote that runs as a MS Works spreadsheet program (I‘m to cheap to pay for Excel). I’ve modified format and tweaked the math to better suit my needs.
On the left side of the screen you input the cartridge data, bullet information, barrel length, and load density. The program takes over from there, selects the ideal powder, calculates a charge weight, and estimates velocity and pressure. It’s not perfect, but it’s typically pretty close. The key is it lets you immediately identify the ideal powder, or range of powders, that will give the best performance in any particular cartridge with any particular bullet. That saves a lot of time wasted experimenting down blind alleys.
Everything to the right side of the screen under “Animal Performance Indicators” is stuff I added, things that I’m interested in, and are not part of Powley’s original computer. There’s a free online version of Powley’s computer that you can access here:
http://kwk.us/powley.html
If you’re interested in internal ballistics it’s pretty fascinating stuff.
