There are lots of programs on the 'net, some to be used, some to be copied and some to be bought. They all give
slightly different results. I tried the one in the NRA book and - while it worked okay - it didn't give me the results I saw on the target. Besides, that's a helluva lot of typing!
The Pesja program that I found at
www.jacksonrifles.com is a spreadsheet which allows you to change any variable and see the result immediately. With it I was able to hold the velocity (which I had measured), the bullet weight (a given) and vary the B.C. to make the 'drops' match what I was actually getting.
We tend to believe the B.C. printed on the bullet box when it really varies from one barrel to the next. I once asked the Nosler rep how they determined B.C.s and was told simply that they had a "ballistics laboratory." What that told me was they were using physical measurements of the bullet to determine the B.C. instead of actually shooting over a measured range. My "amended" B.C.s are close to what the manufacturers claim but different enough to work better.
For instance: I can determine a new B.C. for a bullet by matching the 'drops' at 100, 600, 900 and 1000 yards and then more closely determine what to dial in at 200, 300 or 500 yards. The neat thing is - it works!
A bit of digging also allowed gave me the formulas used in the program which then led me to enter similar formulas into a spreadsheet program on a small, portable computer I own. Now I have the capability of shooting accurately at ranges I've never tried before. All I need is a quick 'fix' with a laser rangefinder, 3 seconds of computing and adjust the scope. Is it right every time? Hell no, but neither am I. Most of my misses aren't due to the rifle, the scope or the computer. They're caused by the nut behind the buttplate.
