I realize that, but all the bullet manufacturers publish BCs for their products. They may not have exactly the same nose profiles, but the BC differences will be relatively minor among manufacturers for the same bullet types and weights. About the only way to possibly do better is to set up chronographs to measure bullet velocity at at least two distances, and then calculate G1 (flat base) or G7 (boat tail) based upon velocity loss. I can (and have) done that, but it’s not too feasible for most. That’s what the bullet manufacturers do. The JBM Ballistics program previously mentioned will calculate BCs based upon velocity loss over a known distance. Some fairly comprehensive BC tables are here: frfrogspad.com/bcdata.htm I don’t really like the idea of using G1 values for BT bullets, but some do that.
Using the Ingalls tables will also work, but that’s sort of an antiquated method. Unless someone has hard experimental BC data available for the specific military bullets of interest, I think using bullet manufacturers’ BC data for roughly similar bullet shapes and weights is the only option.
There are analytical methods to calculate BCs from bullet geometry (ogive type and radius, meplat diameter, length, mass, base type, etc.), but those are prone to considerable error.