Ross is the man when it comes to rifled choke guns. He has several articles concerning the Paradox and Explora guns in DGJ including a reprint( or visa versa ) of the article you are speaking of.
I have heard of a paradox owner or two using round balls in their guns but I don't know the exact results.It is an interesting thought particularly with a 10 or 8. Ballistically, I think the use of a ball goes against the grain of Col. Fosebery's original concept. I think he believed the conical paradox style bullet to be far superior to the round ball extending both usable range and penetration. The paradox chokes also providing more useful shotgun patterns tighter than a traditional ball and shotgun. Leslie Taylor improved on that concept with the Westley Explora guns furthering the useful range and tightening the choke patterns somewhat.