The problem is the group might open up to 6-8 inches, no way to know without shooting...The other problem, it's going to kick the snot out of you...
I shoot 80grs of FFF Goex in my flintlock and have over 20 years...I use 90grs of FFF Goex in my Knight with a 250 Shockwave...I'm 3 inches high at 100 yards and 3 inches low at 150, that's far enough...
Remember the 45/70??? It was a .45 caliber lead bullet with 70grs of black powder behind it...Many, many buffalo were killed with that caliber...