Generally, the loaded shell that is in the magazine will jam with the exiting spent shell as the pump is being cycled. As well, sometimes the breach is very hard to open after you fire a shell. This doesn't happen all the the time but enough to be a bother. Yes, I have kept the gun clean...
Bought a new 535 ATS and I have the ongoing problem of shells of different sizes jamming during the cycling process...Will this eventually work itself out? I have owned a Winchester pump-action for 20 years and have never had this problem with it.