It is possible that the jamming, while certainly more prevalent with the Winchester loads is an issue with the chamber finish being more rough than it should be, causing particuar shells to stick from time to time.

On shotgunworld.com there has been a bunch of discussions about guys with 870 express guns needing to polish the inside of the chamber to keep the gun from jamming.

To the best of my knowledge this should solve your issue


The discussion
http://www.shotgunworld.com/bbs/view...polish+chamber

The fix
http://refugeforums.com/refuge/showt...hreadid=175266