Perhaps not with a round ball, but the conicals, even in 8 bore, weigh several ounces and for dangerous game, are pushed with immense loads of several hundred grains of powder.
Again to reference Ross Seyfried (all the interesting big bore info seems to come from him) he once wrote up hitting some sort of Indian waterbuck (big damn thing, 2,000 pounds or so) with an eight bore shell with a conical. Said it utterly flattened the beast, like hitting a jackrabbit with a 10 gauge. He also reported using the same cartridge on cape buffalo, with pretty unimpressive results. Took two shots and several hundred yards of running, IIRC. In the same article, he reported that the coming of the .577 nitro was a relief for the old hunters, on several counts: more effective on the animal, easier on the shoulder, and no more huge clouds of smoke hiding potential charges.
I used to want a 4 bore badly until some discussions with Steven Zihn about them.
After my experience with the 4, I gave very, very serious thought to buying one of my own. The October Country gun that I was looking at was absolutely huge -- 21 pounds should go a ways toward helping the recoil -- and was designed for round balls, which also reduce the kick. And of course, being a muzzle loader, it could be downloaded. I figure somewhere around ten grains of Fg should be pretty comfortable!
Ultimately, though, I just didn't have the cash to make it fall together. Which was probably just as well, as I can hardly think of anything less practical.
But to have been afield after wild California boar with such a weapon!