velocity 3160 and a bc .648 in the manuals. when i put it in my exbal i have to change the bc to .64 fps to make it match my chart.
It is usually the case that the BCs that corresponds to your drop data will be lower than the advertised number.
If your chronograph is accurate then you should always use the BC of 0.64.
For making a drop chart use 9000 feet and your best guess as to what the temperature will be at shooting time (early morning or late evening).
If you are serious about not enjoying spending a lot of money for a hunt and then having it go badly (and I know what you mean about that) then you will need an accurate wind meter. You can spend a fair amount of money on a stand alone wind meter such as the bottom of the line Kestrel or you can spend increasing amounts of money to purchase the higher up models which will include a a lot more weather variables. A cheap thermometer hung on a pole at camp will get you pretty close to temperature. A good topo map will get you the altitude. If you use an altitude and temperature correction and a humidity of 50% then you are pretty close. The use of barometric pressure is more accurate and that is for sure, but the difference is very small, so we are talking about a small difference.
Some of this is just how much money you wish to spend.