PD. 1in48 should be the twist in that gun as far as I know. it should toss a round ball nice, but is getting fast in the twist, the maxi was made for the TC Hawken, you'll like how it shoots them.
For the round ball tho, you might try to drop the powder down. Start out at 50gr, and bump it up 5 or 10gr at a time until you get what your after.
old rule of thumb as i have been told start with the same grain of powder as the caliber you are shooting and then move up from there.
I use 50gr with the maxi ball when shooting at the range and it shoots nice, I do that just to save powder along with my cheek from recoil, and I notice not different in where it hits the target.
I have never tried but have seen ppl mention to check the twist, by puttting a cleaning rod in it and count the twists as you move the rod up an down the barrel. Good Luck! Ed