I think I read somewhere that if you get muzzle velocity and then get your velocity from a 100 yd. you can get your true bullet coefficient. Is that correct? Does anyone know that formula?

Not real practical. Too many errors on such a short distance. You have a very short time of flight and the accuracy of your chronograph to think about that may be a few%. If you are interested in such things, buy Bryan Litz book.

You need to spread the two readings out over a longer distance. The farther apart the more accurate you will be in figuring your BC. Here is a link to Jbm calcuations page that will help you. http://www.jbmballistics.com/calculations/calculations.html

2 chronies work fine for a good place to start. The only thing you cant get is a drag model but will give you a DANG good place to start. 3 different times this year with 3 different loads I used the double chrony method to come up with a BC and put first round hits in the X ring at 700 yards. My chronies are 300 yards apart. As far as caluclations, it is best to use a ballistic calculator.

You should also check this thread and article out. http://www.longrangehunting.com/forums/f5/berger-bullets-move-g7-standard-bc-bryan-litz-44399/ Very, very informative. -MR