John, why the animosity? I'll answer the question tho....
Besides dropping an 870 30 feet onto concrete, COs has other ways to test the reliability of shotguns,including the 870.
I found one that had the mag follower replaced with a soda bottle cap. Another had a rolled up porno mag hidden in the bbl.
Yet another, on loan from the MD House of Correction, was so neglected it took serious work just to pump it. Several hours of work and some CLP later, it went back to MHC with a report attached that smoked and gave off sparks....
As for personal, non-institutional abuse, one of these here spent lots of hours in salt marshes and goose blinds. To this date, no rust, no parts needed after thousands of rounds shot.