That's an article about greenhill TWIST calcs, and not BC..If you want to get more in depth, this site can help.
That's an article about greenhill TWIST calcs, and not BC..
There is no 'easy' way to determine -actual- BC. Your best bet is to use BC data from Bryan Litz's book: AB for Long Range Shooting
And learn to use the latest in ballistic software in conjunction.