is it the 870 express super mag?? mine started doing it with wal-mart ammo, too.i started to wonder about the ammo, but it seems to work fine in my friends wingmasters and ithicas, so who knows. a retired gunsmith i know recommended lightly polishing the chamber with a wire bore brush hooked up to a medium speed drill, but if yours is under warranty, i'd take it back. if you take it in to be checked over, could you post the results here? i would like to know what they figure the problem is, thanks!!
just a thought...maybe the newer shotguns are chambered a little closer to specs than the older ones so the shells fit a bit tighter?? just about everyone recommended having the chamber polished, and from a little research and replies from cgn members, i've found this problem seems to happen in newer guns only(bought mine new in 04)