I shot a .45 TC Hawken for many years.
Patched round ball and FFF blackpowder.
For a hunting load I used a .445 ball and 80 grains of powder.
You will need to see what works best in your rifle but as is mentioned above you'll probably end up in the 70-80 grain range.
Good luck finding the load your gun likes.
That's half the fun of ML!