if your bess has a vent liner, the coarser powder will probably not be able to enter the inside of the liner and you may have either delayed ignition or no ignition. For that reason you may have to turn the gun sideways and tap the stock a few times to get some 3F from the pan, into the vent liner. My own experience has been that when chronographing 2F and 3F in a 54 cal percussion rifle and about 50 grains charge (can't remember exactly) I had 100 fps slower with the 2F. That suggests to me you will get about 100 fps slower with 1F relative to 2F and 200 fps slower relative to 3F for similar charges in the 70 grain range
cheers mooncoon