How many times have you ever truly needed that third shot? Thinking about going to an O/U for all my hunting. Could you?
I used to shoot waterfowl exclusively and used a Remington 870. When I started upland hunting I picked up an O/U 20g as it was much lighter to carry on the hikes.
Next step was an O/U 12 to extend my time in the waterfowl blind -- no third shot so I was not dropping as many birds and could spend a bit more time over the decoys. Now my hunting is O/U's for all early season waterfowl and switch back to the 870 when we shoot in sleet / snow as that gun can handle the crappy weather.
I have picked up a 5 1/2 lb 12 g O/U that I use for late season pheasants. Nice to have the choices.
