The old foster type slugs will not hurt a rifled barrel. They will not be as accurate as a saboted slug many times,but still good enough to put a lot of deer down. They may lead the barrel up eventually, but a little Butch's Bore Shine or one of the other bore cleaners will clean it up. I've shot a lot of both types of slugs thru Mossberg 500, 835, Remington 870's, Browning B80 with Hastings bbl, all rifled, w/scope and w/o, and didn't find the accuracy gain at 100 yards to be enough to justify the added cost. At 100+ yards they may very well be beneficial,but for most of my hunting here in IA I didn't find it necessary. FWIW