Guys, Thanks for all the info. the reason I asked about invisible rifling is that there was a German made SXS hammer gun on an auction in 12 gauge. It had a single folding leaf express sight mounted on the barrel and a pop up peep sight made into the tang. I thought it surely would have some kind of rifling but the seller stated it was truly a smoothbore. Upon a closer personal inspection he was right, no rifling at all. Yes, I did purchase it and I will get some pics this week. Thanks,,,,Ed