I just saw your previous post, with the new info, perhaps I can at least hazard a guess. Since I suspect the gunsmith looked at the chamber, at least I hope he did, he should have ruled out a rough chamber. It sounds like you have something that is interfearing with the action of the slide. Is the slide staying 1/3 our of battery? If so, can you determine what is holding it in that position? I'm going to assume that you've tried different magazines, right?