I have a 500AB...18 1/2" cylinder bore barrel...stamped "police gun" with the same stocks as OP, but with a bead sight. I got it quite a few years back, from a place in Sacramento that had acquired a complete lot of trade-ins from a L.E. agency. I later purchased a set of "pacs", pistol grip and forend. Over the years I have added a rifled barrel, and many other accessories, and have hunted numerous species of game animals with it. Great slug gun, and it's never failed me. Out of the many choices she has, it's the one my wife will go to if ever there is a need at home...I now keep it set up for just that purpose...Didn't get it for a song, but the $100 price tag caused me to sing a little...Great gun...enjoy!
Tac