1st of all, I don't think T7 will work as well as real BP. If it is all you can get, by all means, use it.
: Drop normal BP loads by abut 20% with the Triple 7. By that I mean, if for hunting, use 80 to 120gr. of Triple 7 for a hunting load for RB depending on the game you seak. For deer, the 80 gr. charge will give a fairly flat trajectory out to 120yds. and will work just fine on deer or antelope. For elk or moose, you need more steam and the RB will still be better then a minnie on them. The only advantage the minie could have is depth of penetration and the RB will make the off side of either massive animal every time, so the minnie isn't needed. On the negative side, the minnies have no point=blank range meaning they have an incredibly arched trajectory, while the RB travels like a lazer in comparrison. To use enough powder with a minnie to make it fly flatly enough, you would need much more than your shoulder or the gun could probably stand - stick with the round ball- it's the best & will also give better accuracy.
: My experience with the PH Enfields is that they (2-band & 3 band rifles) are extremely accurate with RB and very well made, indeed. They need a raised front sight, as do most Zouaves.