The ideal load will only be determined by the rifle itself. Seeing it is a .45 caliber I would start out about 60 grains and then shoot a three shot group. Swab the barrel and up that to 65 grains and shoot another three shot group. Keep doing that until the accuracy and group size is the best you can get. I will guess that it will come in somewhere around 70-75 grains. Just so you do not get too discouraged, some rifles even though they are Thompson Center do not like maxiball or maxi hunters. It might not ever produce an excellent group. I doubt that will be the case. You might also want to consider putting a wonder wad under those conicals. It will many times improve the group size.

Your rifle should also shoot roundball excellent. I can understand your desire for a larger bullet if hunting deer, but shot placement is the key. If you can not hit what you aim at, no bullet in the world will do the job. Yet, a will placed .45 caliber roundball at a reasonable range will kill deer. And I bet that is a lot of fun to shoot....

Another large conical you might want to try is a .45 caliber No Excuses. The .50 caliber shoot real good in my rifles. Perhaps the .45 caliber they make would do the ticket in yours.

Good luck with your rifle..