Chrono to get velocity, then shoot downrange to get actual drop at a known distance based on a shorter range sight in distance. Play with the BC in a ballistic program until it matches your test, then you should have a reasonably accurate drop chart for other distances.
Maybe sight in at 100 or 200 yards, then check drop at 600.
ETA- Winchester USA 147gr FMJ has a BC of .421 according to the JBM Ballistics website, so that might similar to your bullet.
Maybe sight in at 100 or 200 yards, then check drop at 600.
ETA- Winchester USA 147gr FMJ has a BC of .421 according to the JBM Ballistics website, so that might similar to your bullet.
Drifter