Partner,
You should (imho) instead of the Maxi-Ball from TC, try the Maxi-Hunter. As suggested the Hornady Great Plains bullet is also to be looked at.
I have a New Englander, and you'd think that since it's a TC product that both types of TC bullets would work well, and you'd only go to the Maxi-Hunter to go heavier. Well, I found that Maxi-Hunters and GPB's worked very well in my New Englander, but the Maxi-Ball..., NOPE.
As suggested, start with powder equal to your caliber, so 50 grains. In my case I was looking for a deer hunting load, and in my state we have a minimum powder load of 60 grains so I started there. I found that like my flinters, 70 grains of 3Fg worked very well with Maxi-Hunters.
LD