Published data from Lyman's Black Powder Handbook (2nd Edition - page 287) shows 7-1/2" bbl ROA shooting a .457 round ball over 40 gr. FFFg to 1076 fps and 370 ft/lbs at the muzzle.
Stoutest load shown is a .457 190 gr. Buffalo Bullet conical over 40 gr. FFFg to 1035 fps and 452 ft/lbs at the muzzle.
Based on my history with ROA's, 40 gr. FFFg is almost the maximum amount that can be loaded into a ROA cylinder chamber, with a lubed Wonder Wad on top of the BP. None of my CAS FFFg BP loads ever reached much over 900 fps on my chrono back in 2005.
Suggest you compare the Lyman published data against .357 Mag or .44 Mag factory loads.
ROA's make a lot of noise and smoke when shooting with BP, but "bear repellant", borderline.