I had some of the same issues. Make sure you don't have any kind of oil, grease. case lube or anything on shell casings. This will cause sticking sometimes. Here is something I did, I still have one stick every now and then no matter what. Get a dremmel tool and put on one of the small cutting discs and and cut a little notch . Cut it where case rim touchs the barrel , I keep a small eyeglass screwdriver in one of the shell holders that goes around the stock, just in case. Its a b*tch to carry a cleaning rod in case it happens. you can pop it out easily with the little screwdriver in case it does happen when you least expect it.
Good luck.