It'll be a touch over a week yet before I can say how the stuff performs in a muzzle loader from personal experience. I do know a friend of mine left his measure set for 55 grs of 2f goex, and with that same measure of Olde e he was getting about 130 fps more velocity in his 54 flintgun.
In my 44-77 sharps 76 grs of 1.5 behind a 480 gr paper patched bullet is driving at 1307, same bullet and 78 grs of KIK 1.5 is about 1225, and 77 grs of Cartridge does 1180.
70 grs of 2f old e in a 45-70 has been reported as hurling a 480 gr grease groove bullet at 1380, and 2f Goex will send that same bullet right at 1210.70 grs of the 2 and 1.5 both sail a 535 postel out of a 28 inch barrel 45-70 at 1225 fps.
This stuff is seriously fast, and to keep muzzle velocity the same, and in some cases accuracy,one is going to have to drop powder charges.