Good luck! That target is going to look really small at 300 yards. Should be interesting.
Years ago I purchased a T/C Black Mountain Magnum .50 caliber. Those rifles even though traditional in style basically have a T/C Omega barrel on them. They have a 1-28 twist that I discovered must be swabbed between shots. But I threw a scope on it. I was shooting some impressive groups with it at 100 yards. But never thought of 300 yards. If a person was shooting a 200 grain Shockwave 40 caliber with 100 grains of black powder ... what would you guess would be the hold over at that kind of distance? Out of curiosity.