I would suggest trying a heavier projectile. ANY 245gr 50cal bullet is a poor choice for anything larger than a coyote.

Federal has a new 350gr lead bullet.
https://www.muzzle-loaders.com/feder...350-grain.html

http://www.midwayusa.com/product/353...ain-pack-of-15

I dont like Powerbelts but you might try a heavier one like
338gr Platinum Aerotip http://www.midwayusa.com/product/242...ProductFinding

348gr Aerotip http://www.midwayusa.com/product/242...ProductFinding

I would also suggest trying a lead conical. You might get lucky and have a T/C that will shoot a typical lead conical. These may seem heavy but you don't need a 100 gr load. 70-90gr is usually plenty for big lead.
http://www.muzzleloading-bullets.com...es/Page319.htm

Another option are Thor copper conicals but they will require a sizing pack to know which size fits your barrel.
https://www.thorbullets.com/