Have had scopes on 2 Valmets in 9.3x74r,30-06,243. Used Leupolds in all cases. Also had a Leupold on a 30-06 Win O/U. Factory mounts in both cases.Scoped a Chapius 9.3x74r S/S with a Leupold. Took a Ruger quarter rib and cut and machined base blocks to fit in precut rib of Chapius. Used Ruger rings. Worked perfectly even matched the screw holes in the new blocks so didn't have to drill any new holes in gun. Could not use low rings as you could not get to the top lever had to use medium or high. Also scoped an Otto Geyger 8x60rs with a Swarovski 1x4. Made custom block to fit in rear claw base and made new base to fit in dovetail where front claw fit.Bases were for Leupold Dual Dovetail rings. NO mods to gun and it could be returned to original very simply.All worked perfectly and had NO problem with regulation. In fact until I saw thread here on this forum years later I never even thought it could BE a problem. Such is ignorance (and luck I suppose). I also have a CZ combination in 12ga/7x57r that is scoped with a Leupold and CZ factory mounts. It's not particularly accurate but sufficient for plains game.