the little dovetail inserts that your screws go in are probably shifting around(common). You can center them and pin them on the sides of the dovetail with a hammer and punch or you can epoxy them in place. Since so many resell barrels, the pining method would not be used. I don't sell so I pin mine. One other way(acceptable) would be to remove the insert and tap down on the dovetail(at the center) and reinsert the insert to the center position. Pat
