RE: How do you figure the BC?
Stick in 0.2 for the BC of a ML bullet and that will get you close enough to get on a target at 200 yds, and adjust from there.
Published BCs for ML bullets are horribly inflated from what I find them to be when I shoot them. For some reason they are much more honest with centerfire bullets.
What I usually do is shoot the gun and determine the real-life drop at 100 and 200 yards, get the velocity off my chrono, then put it in the calculator and play with the BC value until it matches the real world. I use this to estimate 300 and 400 yd drops, and am usually pretty close.
The only BC that matters is one determined as I do above. The numbers they publish are so far off I would never hit a target with them.
Also, scope height measurement etc get important as you get out to around 300 yds.
The real way to determine BC is to use two chronos, one at the muzzle and one at the target.