I think you're describing a 12 gauge slug gun. Fine at close range on soft skinned game. Stuff like elephants, rhinos, and cape buffalo, I'd still want a .416 Rigby with solids.
I know, I love my Mossberg 835! There is some really nifty large game killer ammo out there. Even for a smoothbore, there is Dixie triball. I just can’t help but think what gun innovations will be out in the next 50-100 years.