In 1999, I purchased a brand new Rem 870, Light Contour, 12 gauge shotgun with screw in chokes. I would like to buy a second barrel to shoot slugs (smooth bore,no rifling,cylinder bore). I know the general rule is that 870 barrels can be swapped out with in gauge, but I thought that I read years ago that when it comes to the Light Contour frame, it could not be done. I'm I wrong ? If so, where can I get a slug barrel with adjustable rear sight ? Thanks.