There are a few ways to determine the BC of your bullet. One is to shoot through a Chrono at Two different distances and use a calculator like JBM - Calculations - Ballistic Coefficient (Velocity)
and then you will know. However, I never liked the idea of shooting over a chrono 300 yards away (the longer the distance between the two readings the more accurate your BC will be.
Another way is to simply sight in dead on at 100 yards and measure the actual drop your impacts are a several different ranges. Lets say you measure at 100, 300, and 500 yards. You will be aiming several feet in the air by the time you get to 500 yards. Last summer I tested my rifle in this manner and simply took a 3' x 3' piece of cardboard and just had an "aiming point" raised above the target. I'd measure the distance between the aim point and the impacts. Then you go back to your balistics calculator and play with the bc (only the bc) until you find readings that match your actual results. Then you can use your balistics calculator and test your results at farther distances.
The key to doing testing is to have a "control" and to only adjust one thing at a time - trying to focus on one variable. So, never adjust your scope when trying to find the initial BC because your scope adjustments may not be exactly what they are advertised as.
Good luck, Mark.