I've got an old Marlin bolt action goose gun, 12 ga.

It's got a 36" bbl, and if you put a 5X5 piece of cardboard up at 90 yards, shoot a 3" 00 buck magnum through it (which has 15 pellets) and you will count 13-15 holes (depening on how good you are with it).

At 50 yards or less, I think it'd knock an elk right on his butt. Of course, he might get back up. None of those pellets would probably have enough energy to individually kill him.