My Browning A-5 .20 has killed more ducks than any other gun I have, and its a 2 3/4" gun. I' ve killed black ducks landing in the blocks, teal in the marsh, I' ve pass shot mallards (Deadest duck i' ve seen was with the .20, an old mallard drake at 40 yards) so the .20 is a good gun if you pick your shots.

Pick A Spot
Matt Whitehair