Found this post from 2009:
So I picked this gun up for 250. Oddly enough, the safety is the old variety that isn't as serrated as the new ones and it's metal. The trigger is a weird kind of plastic, harder than the new versions but just...different. 18.5" barrel, riflesights, no real blemishes on stock or forend. Cylinder bore, parkerized finish, Capacity 5+1, integrated sling swivels and MOSSBERG 500ATP stamped under receiver. I looked down the barrel and it was full of cobwebs - I don't think it'd ever been shot. It'd just SAT somewhere. Even had a lot of near-hardened cosmoline in the chamber when I opened her up. And if that wasn't enough, it came with 3 inch mag steel shot shells in the tube....they'd probably been there since the 80's or 90's or whatever timewarp this little tank fell into. It's quite stiff, even after a fieldstrip clean and lube, so I think it needs some trigger time. After cleaning barrel was SPOTLESS. It's also seeming to want to double feed, any idea what could cause that? Possibly a stiff spring from having shells in it for years? Also, I can't seem to find out how to take the mag spring out, or if I even can. It isn't like a 590 where the retainer just prys out. Anybody know? I would've done this deal in a heartbeat ten times over. What do you think?