FFG is the stuff I use!
I strongly suggest you get to Wholesale Sports and buy Paul mathews' book on BCR loading.
The powder charge is only one part of the equation of an accurate load, but if you get the mix on your lead correct ( normally about 20:1 lead to tin)
and your bullet lube/base wad correct, you can achive some incredible shooting with the black powder cartridges!
I compress 68 grains of FFG in my gun and use a beeswax base wad with a modified Mathrews lube.
With this combination in Blackman's H&R Buffalo Classic, were able to shoot sub MOA groups at 100, and 200 meters.
Oh, get an "M" die for your finishing die as well as your decapping and and seating dies. Oh, and a MILD primer not a magnum or hot standard - BP loads work better with them.
Cat