I bought a 20 gauge smooth bore nef shotgun a couple of years ago and tried 20-gauage remington sluggers in it last year but without rifle sights the birdshot barrel proved unreliable in aiming.....but I had a 12 guage rifles nef barrel laying around from years ago with the old square notched click adjustable sights.....and I had a plethora of brenneke ko knockout slugs....so i tried the 12 gauge bbl on and it locked up tight, fired it once from the hip and it held tight so i tried it at 25 yards and then 50 yards and it shot almost as well as the 45-70.....not bad for a second hand leftover barrel and a strange frame and buttstock.
Gotta bench rest it and adjust the windage as it shoots about 4 inches to the right but it prints a decent 4 or 5 inch circle at 50 yards from a seated position so I am more than happy right now......