Here's an update about the 870 Express models... I talked to a gunsmith about the supposed "870 Express problem". Some models have it, some don't...
What it is: Leftover residue and gunk and Lord knows what from the manufacturing at Remington. It can be found inside the chamber and worse - even down a few more inches in the barrel from the chamber. The plastic shell casing will occasionally get "hung up" after the shot is fired, causing the 870 Express not to extract the shell - not without brute force from the butt stock to force it to eject the spent plastic shell casing.
Remington is so busy trying to make 900 Gazillion Remington 870's that their quality control is starting to slip a little, and some Express models slip by with residue and gunk still left in there. The "dowel rod and ultra fine steel wool" trick takes care of the issue quickly, and you'll never have a problem again.