Since going back to parkerizing we've had a few similar problems. Parking is not as smooth as black oxide, so some chambers have been sticking occasionally. What I do is chuck a chamber brush in a cleaning rod section in a drill and run it in & out of the chamber for approximately 15 seconds and that should take care of the problem. What is actually happening is the park is getting in and coating the chamber and causing the empty to stick. Running the chamber brush is polishing out the excessive coating.