If your TC Hawken is one that has shallow groves and a 1 in 48 twist, you will get better groups if you drop your charge back to around 50 gr. You might try using FFF black powder, .490 and .495 round balls, .015 pillow ticking and spit for lubricant. Shoot some three shot groups every 5 gr. starting at 45 gr. and increase the charge upward to see where the rifle groups best. You should find a sweet spot where it shoots the smallest group, and then starts to increase the group size as you increase the charge. As an example, my .54 shoots one elongated hole spot on at 25 and 50 yards, and 1 1/8 inch group 5.5 inches low at 100 yards using 70 gr. of FFF black powder. However, the same rifle will only shoot an 18 inch group at 100 yards using 110 gr. of FFF black powder. I had a friend who use to beat me like a drum that used one of these TC rifles (45 cal.) using .445 cal round ball and pillow ticking with 50 gr. of FFF black powder. He was a great marksman.
Working up a load takes time, but it is fun shooting as well as gets you familiar with the feel of the rifle. Good luck with you shooting.
Roger Sells