I don't have a rifled barrel, but borrowed one from a Shooting Budd and tested the theory for myself...
A rifled barrel produces HORRIBLE patterns with shot loads. The rifling spins the shot column, and gives you a classic "doughnut" pattern. If you have the shot loads with the plastic 'cup' around the shot, lotza spin and doughnuts. If you have 'un-cupped' loads such as Wolf and some other buckshot ammo brands, the rifling gets leaded up very heavily, and shot is deformed by the rifling...again resulting in blown patterns.
I tried this with 00Buck, #1Buck, #4Buck, #4bird & #6bird. Very little difference...all patterns were lousy.
Plus spent several hours 'un-leading' the barrel.