^agreed. The 870 Youth Express in our family has an amazingly-smooth chamber, but my nephew's 12ga needed some TLC. Still, the best place to start.
After reading this whole thread, a few things occurred to me...maybe worth asking the OP?
1. Does this occur all the time, or only when the chamber is hot? I've seen spent hulls get sticky in a variety of guns~when they get hot
2. All shell types, or just some? Personally, I don't dwell on this or bend to a fussy shotgun's menu preferences. I'd rather remedy the issue so it can eat everything it's fed.
3. Is the OP comparing pumping effort in his 870 to the pumping effort required with a Mossberg? Reason I ask...I think Mossberg 500s seem to take less effort to cycle, though I only just got my first 500 recently. Not sure why. Anyhow, it certainly feels like it's less effort. My experience owning an older Ithaca 37 is the same, and comparable to a buttery-smooth, well-worked-in Wingmaster. I've never owned/shot an Express that seemed to take too much effort, in fact, I'm usually surprised at how little they require for an inexpensive pump.
The only 870 Expresses I've ever seen that failed to function were guns that were treated terribly. I have to wonder how much of the negative press they get has to do with people treating a $400 shotgun like crap, then complaining that it doesn't function like a Wingmaster they'd always treat well. lol