I used Douglas barrels on all of my flint locks and my load has always been 90 gr of FFG in the .45's because it is most accurate.
I use 100 in my .54 (RB) but when I shoot 200 meters I up it to 120 gr. (RS Pyrodex for competition.)
BP is funny and some of those loads will not increase velocity.
There is a point when increasing the charge will stop any increase in velocity and you can actually go backwards. Powder weight has to be added to ball weight because you are pushing more down the bore. There is a point when a lot of unburned powder is blown out the muzzle too. It takes a long barrel when you use more powder.
Some of today's rifles have awful short barrels but most guys use substitute powders.
I will not use FFFG in my rifles.
