hello guys,
i have had a 20 ga 870 for several years and have put over a thousand rounds through it with absolutely no problems. i got an 870 12 gauge probably a year ago and have probably put 400-500 rounds through it. i thought that as i shot it more this problem would stop....but it hasnt. when i start shooting i will take a shot and the fore end will lock without letting me eject the spent shell. Is there anything i can do to stop this? thank you

Rough chamber. Recent Expresses are notorious for this. Steel wool on a rod chucked in a drill and polish the chamber. You might even attempt to try, if you dare, the finest grade of sandpaper that the automotive paint shops use and do the same.

Polishing compound on a shotgun cleaning mop on a section of old cleaning rod chucked into a drill should work as well.

If it is a rough chamber, an automotive drum brake wheel cylinder hone is the answer. The small spring loaded straight stones polish the chamber and remove any ridges.

Wow Virginian most people(nowadays) probably have never seen a brake cylinder! Good call.