Lead slug won't. Copper jacketed shouldn't, since copper is much softer than steel. Besides, most slugs sit in a plastic cup if I recall correctly.
I just tried out the Remington Sluggers. They are all lead and pre-rifled for smoothbores like mine. They were pretty accurate, but I only shot three before my shoulder started aching.
If you're asking if lead, foster type slugs through a smoothbore barrel would cause scratches, I might be in big trouble since I've qualified 47 officers so far this month with slugs and 00 buck! You're ok.
