I'll state my experience with #4 bismuth 1 1/4 oz. handloads at about 1200+ fps. I shoot them out of an overbored Fox with extremely tight chokes. I can kill a big mallard dishrag dead settling into the dekes at 50 yards pretty easily with that gun, sometimes a good but farther. Killed one a couple years ago going straight away at about 45 yards, and that is the hardest shot angle with which to anchor a duck. If you don't break a wing you have to drive the shot from his rear end all the way up into the vitals ..........tough job to do.
There's no reason a muzzleloader w/black won't kill just like a breechloader w/smokeless if the velocity, shot size and pattern density are the same. But, the devil is in the details.