Lots of dry fires can cause the firing 'pin' to put a ding where the round feeds, causing the problem you described. A dremel fixed it for me. mandatory disclaimer. Don't take power tools blah blah blah. I did it because it's only a .22 and I'm confident I could fix it. I deburred the edge of the chamber, then polished the inside where the round enters with some jewelers rouge. Look at it, you might be able to see the ding from the firing pin strikes. Also had the same issue with my 597, fixed it the same way.