I've read a couple of articles about ballistic coefficient in the past couple of years where the experimenters measured the muzzle velocity with a chronograph, and recorded it downrange with a second chrono. The actual BC can then be calculated with a formula using the velocity remaining and the distance. Derrick Martin of Accuracy Speaks, in Mesa, Az. did it with the second chrono placed at 500yds. I'd love to find the actual BC of several of my favorite bullets in this way, but none of my friends will lend me their chrono's to put downrange! Interestingly, Sierra rates their 22 cal. 80gr.MatchKing at .420, while Derrick's tests showed it with a BC of close to .480. Sierra's ballistics gurus explain it this way. The BC of a given bullet will change with atmospheric conditions and altitude. So, even if you take a computer to the range with you, and the best ballistics program in the world, you'll still be using a SWAG(Scientific Wild-Ass Guess)trying to come up with the exact trajectory of your bullet.