Slide Rule Ballistics
Date: Apr 11 2019
The old expression, “You’ve come along way baby” surely applies to our handloading hobby. While we are used to turning on the laptop to compute a test load for our rifle, years ago the closest thing to this was the famed Powley Computer for Handloaders.
In the past, most, if not all, of the data we needed was located in the pages of a commercially produced loading manual. These “bibles” were the main source of information on the complete handloading process, from purchasing brass right up to finally seating the bullet in the case. Unless you knew someone high up in the manufacturing chain who had chronograph information, you were strapped to a loading manual, and later, perhaps an Oehler chronograph was available.
However, before all this was the Powley Computer for Handloaders and the Powley PSI calculator for estimating pressure readings. Additionally, Speer offered a Ballistics Calculator that gave the astute handloader the ability to estimate the range in yards and bullet drop. All three were easy to operate, made from sturdy laminated cardstock, and after all these years I still have mine.
Research shows that three men had a hand with this novel slide rule. Homer Powley was the brains behind this little invention; Bob Hutton had the Hutton Rifle Ranch for testing; and Bob Forker — a retired handloading writer — worked for a company that by chance made slide rulers for the general public. Together they developed an important tool at the time for the serious handloading hobbyist. In the past, I did work some loads with the Powley Computer with some amazing results.
From the beginning, I took note of the details this little unit offered. For a complete evaluation of a project, the slide rule shows the case capacity in grains of water, grains of powder, the ratio of charge to bullet weight, bullet in grains, sectional density, powder type (IMR powders are used) and of course the caliber and barrel length. The PSI calculator is also detailed pressure in thousands of pounds per square inch.
It would take a complete article to explain the Powley Computer, but if you want to pursue the details, look at Handloaders Digest 8th Edition published in 1978, I believe. While these slide rules are not widely available now (I purchased mine years ago), but I have seen them advertised on Ebay and other online sources for around $50.00. The slide rules are fun to use and accurate to boot.