I've seen quite a few Marine Magnums around here (commercial gun cleaning is one of my sidelines) where not only are they used in a salt water environment, but they shoot truck loads of corrosive cracker shells in them too, and these guns seem to stand up very well. The only recurring problem I've seen is cracked barrel guides in the receiver when guys who don't know much but think they do, get rough reassembling them. Although I've seen shell stops come loose from their stakes in older, heavily used 870s, I haven't come across a Marine Magnum to suffer from this yet, we'll see what happens once they're 30 years old. While I prefer the Mossberg 590, the Marine Magnum runs a very close second, and at this moment there's more after market stuff out there for it.