I have a 870PM that when you try and rack the slide to chamber a shell the shell comes up on the lifter to the exact midway point in the port (so that the nose of the shell is 1/2 from chamber and the bolt is forward enough to show the extractor in the port and the shell is almost horizontal with just slight nose up of parallel in the port and you can see the lifter under the shell) and the action STOPS. If you then apply great force to the slide it will then load the shell. This occurs not everytime, but often to 1/3 of the time. I have checked for the shell hanging up and can slide easily a business card around the entire shell except at the shell rim.
What I have noticed is the ejector spring is not sprung up off the frame as much as it should be which could cause an ejection problem (but is not causing an ejection problem) and should make the shell passing by it to load even easier as it does not make spring loaded contact with the shell. So I do not see how it could be the issue unless the ejector springs secondary job is to keep the shell from making contact with the ejector rail during loading and the shell is friction binding on the ejection rail. That ejector spring is normally so weak I can't imagine this is the case, but maybe.
Ideas?
God Bless and Happy Thanksgiving!