Re: power belts?
My experience is fairly limited but I'll share my one and only flintlock kill with a Powerbelt.
I'm shooting the 295 gr hollow point pushed by 100 grains of Pyrodex out of a TC Firestorm. No accuarcy complaints at all, it groups well for me.
I shot a doe Dec 26th, 50 yds, bullet hit her just forward of the shoulder and a tad above midline. She dropped in her tracks. Upon processing, the bullet hit the bottom of the spine and deflected down and back, lodging in the opposite side shoulder. I will add the doe was ever so slightly quartering to me when I shot.
The bullet did not exit and was mainly whole and had a mushroom shape, it did fragment a little. I suspect hitting the opposite side shoulder stopped the exit.
My friend shot a doe 2 days later. Same gun, same load, double lung, 55 yds. That doe also dropped in her tracks and the bullet exited, and the exit hole was rather large.
Not sure what shape the bullet was in, we never found it of course.
Hope my experience helps, limited as it may be.