I find everything Gator Weiss states in the very first post of this thread to be accurate and true to what i believe. Having said that , the mossbergs in my life have been smoother to operate , more problem free and something i find valuable in a sd / combat sg is that a mossy is somewhat lighter. Points faster. Again ,all Gator Weiss's points factored in ,my mossy's are more to me than my 870's. I would'nt sell any of them except (lol) a 5 yr old ,15 rds fired ,mint cond 870 marine magnum with a knoxx breacher's grip on it because of the nickel clad color. No other reason exsists. Shoulda bought all black but it was one year later remington started making thier marine mags in a black waterproof finish ,which i have. The coatings name escapes my memory at the moment but it's just as sea worthy as the silver ,nickel finish i wts. Either way ,both awsome sg's.
In general i think the of the 870 as a heavier duty , rougher cycling sg than mossberg's 500 butter smooth ,lighter sg.