B.C. ought to run about .2 or so. Just compare to the closest weight jacketed with a similar profile (which is probably the Sierra 300 gr., Speer 300 gr, or Hornady 300 gr. - you could probably just average the 3 and be close enough!). Don't get too hung up in BC numbers, they can vary quite a bit from gun to gun and even when the loads are tweaked a bit, as sometimes the bullets don't stablize as easily under different circumstances and this can increase the drag quite a bit.
This should get you close, and if you want to figure out your sights for long-range shooting, try them out and see what the actual results are.