Does the gun come with a users manual? I have had 2 .58 TCs but I don't want to recommend loads too stout for your gun.
Both had a 1-48" twist. The first gun was accurate with everything ... when it went off. It wouldn't fire reliably. The replacement gun fires reliably but is horribly inaccurate with all conicals and not all that great with round balls. Good enough I guess but sure as hell nothing to write home about.
Anyways, in the first gun, I worked up to max shooting groups with both pyrodex and FFg, round ball and conicals, and in all cases I found the hotter I loaded it the better it shot.
I hunted with it with Pyrodex RS or Select, whatever I could get, didn't matter, and TC's 555 grain conical. That was good for about 3-1/2" groups at 100 yards, about as far as I want to shoot. I never hunted game with it with round balls. While not most accurate, I found a really useful round ball load which used 60 grains of FFg under a patched round ball ... this hit to the exact same point of aim at 50 yards as my heavy conical hunting load so I didn't have to adjust the sights. The more accurate max load with a round ball was off a foot or more.
The current gun won't keep 5 consecutive conicals on the same dinner plate at 50 yards no matter which I choose or what I launch them with.
It's adequate at 50 yards with a round ball but like I said, nothing to write home about. I've tried various charges, both FFg and Pyrodex. It does its most accurate shooting with 120 grains of FFg.
At 289 or 290 grains, that's probably adequate but not satisfying or comforting the way a conical is.
I've thought very seriously about ash-canning this gun, too, but the market has changed and the guns I like are no longer available new. What is available comes with features I don't want to have. I may get out of muzzleloading once I manage to kill an elk with one.