375CT,

There are lot's of analytical and numerical ways to estimate Cd directly. However the method I just told you is one of the most accurate and still very simple.

If you don't know the actual BC of your bullet use measurements and drawings from Litz's book to estimate form factor and calculate BC from it (I have done this numerous times and usually get the BC right with the accuracy of 3-4 % which is better than I can manage with CFD). All you need for this method is good reference bullet. When you have BC then just use G-drag curve as shown before to calculate Cd.