I typically use an autoloader for pheasants when hunting in Minnesote for a couple of reasons. First, typical pheasant habitat is swamp/marsh lands which often adds ducks to the options when the water is not frozen. This necessitates non-toxic shot and my autos are the only 12 ga guns I have that will handle steel shot. I guess my clays O/U is steel safe but I don't wish to subject it to the rigors of marsh hunting.

The second reason is the third shot can be helpful in finishing off a winged rooster. That third shot will spook fewer birds than a dog chasing after a cripple. When a hard day of hunting produces two to three opportunities for roosters one does all they can to keep the odds on their side.

These opportunities may come all at once as pheasants tend to flock up late in the season. One might tramp all day without seeing a bird and then have dozens of birds get up with one step. It is a very real possibility those will be the only birds you see, particularly as one is often hunting public land, so having extra rounds can be helpful. It falls much in the same vein as hunting mountain chukars as mentioned earlier.
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And we all know the quintessential upland bird hunting experience occurs following a pointing dog...;)