my buddy put a rifled choke on his 12 ga. 870 this year. He went from plate sized 9-10 in. groups @ 100yds down to 3 inches.
Good to hear some first hand experiences. 3" groups are pretty darned good, I wasn't sure just how much just the rifled tube would help, but that is certainly respectable! You also answered the other question I had in my head, and that was whether or not you could shoot sabots with that setup. I would have guessed yes, but that confirmed it. Sounds like Alias just needs to sight that gun of his in and put in a little practice time and he should be good to go.