I have had the same type of jamming in two different 870's. I first was back in '95 and I sent the gun in for repair. Remington polished the bore and it had done it since. Then second one happened last week. I took the the barrel to a local gunsmith who has seen this type of manfunction before. He polished it out, but I haven't had a chance to test it yet. I'll let you know what happens.
Life's too short to carry an ugly gun.