DocD, I guess it doesn't surprise me that a rifled barrel improves the accuracy of a rifled slug. I'm curious what you found about range. I'd assume that even out of the rifled barrel, the rifled slug wouldn't keep up with the sabot.
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As for the original question, you can do it, but if you spent the money on a rifled barrel, why not shoot the ammo it was designed to work with out of it? It's expensive, but after you figure out what slug your gun likes, you won't have to spend that kind of money every year -- just enough to get a little practice and confirm your still sited in.