You are wrong. I have a Mossberg 500 Rifled Barrel with fober optic open sights with no scope mount on my Mossberg 500 right now. I bought it 2 years ago from Fleet Farm in Marshfield Wi.I paid 155.00 for my rilfled slug barrel Ill post pics tonight of it. And yes this is a Mossberg barrel, not after market.
ORIGINAL: 4RCH4NG3L
Mossberg doesn't make a rifled slug barrel with open sights for the 500 or any other gun, they all come with scope mounts. You might find an old one..maybe, but I've had a 500 for years and I've never seen one but perhaps some aftermarket company makes them. if you want one bad enough it will run you about $125-150. and I would dig on Google for it.