YOU CAN SAFELY USE plain lead rifled slugs in your rifled barrel, but these tend to lead up the bore sometimes, causing accuracy to drop off after a few shots. Also, leading is sometimes difficult to remove. I recommend using slugs like the Winchester Partition Gold, rather than Foster-type, or other soft lead slugs, if you have a rifled bore. Granted, these lead loads are a lot cheaper, but why bother with a rifled bore if you are not going to use the proper ammo in it??

Keep yore powder dry!!