I am looking to get a slug barrel for either my 12 or 20 gauges 870 remingtons and would like to be knowledgable about it before I get waist deep.

My questions are:

[ul][*]Are slugs or sabot slugs made to come out of rifled barrels or smooth bore? Which do you find are more accurate. I know, different guns pattern differently.[*]Is buckshot made to come through smooth bore or rifled barrels?[*]What is a price range I should be ready to pay for a rifled barrel?[/ul]
Thank-you for your input, grealty appreciated.