Here's a beaut. Mounts to the RAS, it's a KAC Masterkey, a rem 870 super mag that takes 3 1/2" shells.
Comes with a big pricetag though, $1500.
[url]http://pjs-steyraug.com/LAWENFORCEMENTWEAPONS.html[/url]
[img]http://albums.photopoint.com/j/View?u=1265513&a=9363851&p=33534006[/img]