Re: True BC of a 220MK
I'll be running some through the Oehler 43 out of a 300 Ultra in the next few weeks, it will give a true BC for that speed and conditions.
If you have a GOOD cronograph and if you start with perfect 100 yard zero groups, then go to between 500 and 700 yards and measure the ACTUAL drop. Compare to a drop chart at the temp etc during shooting and now you have something to go with to click on out beyond this too.
I have always used a sheet of plywood standing vertical covered with butcher paper. Remember to measure the center of your groups for accurate results.