Seems it favors the sabot, but the right bullet/lube combination should still give good accuracy. Never had this specific model, but had lots of experience with their Hawken having the same twist rate. The Maxi-Ball shot very well in mine and had to be pre-fouled before hunting.
With that short sight radius and the factory irons, you would have to be an exceptional marksman to have guilt-edge killing accuracy much beyond 100yds. So, the super-fancy SST’s, PRB’s, Scorpion PT’s, Tipped MZs, etc are not required. A full diameter bullet that you can get to shoot well should thump anything within the range of your accuracy.
Maybe try the Powerbelt (normally not best out of the barrel size produced by T/C), Hornady FPB (these shoot well) and the Harvester Sabertooth with NO lube at all. Light spit patch clean between shots. Test in 5gr powder increments to see exactly what your rifle likes. You “should” be in the 90-110 grain range, generally. Stick to Goex 2F (very hard to get) or the Pyrodex Select for your sidelock. We always used Rem or CCI caps, but have no idea what is available. Good hot caps are a must. Clean the barrel dry and pre-foul before hunting.
If you want to get really gnats azz, carefully measure your powder by volume and then weigh it on an accurate grain scale. They will NOT be the same numerical value, so be advised. All corresponding charges are then weighed on the scale to meet the charge measured on your volumetric device. Then, pay attention to how tight you put that bullet on the powder charge.
Here’s the best target that I have found for ML load testing at 50yds. Take a 6 o’clock hold as you would for any target shooting to get the best finite sight picture. I use white/black labels to reuse targets over and over.