Plain, ordinary slugs are often on sale after deer hunting season, especially in areas that only allow shotguns to be used.
At reasonable distances, they seem to do quite well in rifled barrels.
Try them and see if yours likes them, too.
What's to lose?
They are about $5 to $7 per box from the mail order houses.
http://www.cheaperthandirt.com/ItemL...spx?catid=6071