Re: true bullet coefficient
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.
Long range shooting is a process that ends with a result. Once you start to focus on the result (how bad your last shot was, how big the group is going to be, what your buck will score, what your match score is, what place you are in...) then you loose the capacity to focus on the process.