One lad on here got his .72 working with 175gr. of T7, seems to me, using some form of slug.

I would be attempting to get it to work with patched round balls.
The muzzles need to be re-crowned as they are merely machine cut, so have sharp corners.
Your thumb and emery of wet/dry paper on the end of your thumb, rotating and then every 15 seconds or so of rotating your thumb, rotate the barrels 180 degrees to keep your 'smoothing' concentric.
It's easy. If you need or want to see what they should look like, PM me your e-mail and I'll send a couple pictures.
The smoothed and rounded crown allows the use of snug loads that not only shoot better, but also allow using loads that do not require frequent cleaning while you are shooting.
Real Neetsfoot Oil works as a patch lube for hunting. Never use a water soluble oil for hunting nor for storage.