There's a twist problem. Large caliber round balls work best with a very slow twist, something on the order of 1-100".Rifled shotgun barrels have a far faster twist.
I've shot a good many .735 RBs through a custom rifled 12 gauge Martini, a Tracker II, and a Remington 870 with a Hastings Paradox tube. I'm happy to get 4-6" 50 yard groups. Think all those have about 1-38" twist, but don't hold me to that.
Never tried brass cases because shotguns hulls will take the .735 ball and I have some pressure tested data courtesy of a long ago Gil Sengel article. I sure don't need more power because the loads I am shooting have been known to make my glasses fly off.