Yeah don't use a rifled barrel, you wont get very good patterns that way.
The standard for an acceptable pattern is 100 pellets in a 10" circle at any given range, although some people would say it is 80. Either way, you and your friends falls very much below the standard.
Personally, I would go with an Indian Creek choke tube, and Hevi-13 3" 2oz #6's and see what kind of pattern it gives you.