Being a gunsmith I find the old Mossberg 500 to be the most reliable pump ever made. It had onlu one little fault. The idiots switched from a metal to a platic safety button that used to go bad frequently. I'm toting Mavericks these days.
If you have the 590, it comes with a lug. It accepts AR bayonets like the Ontario M-9 and other M-9 bayonets.... http://www.m9bayonet.com/
I'll have to get an updated picture of mine. It's a 590A1, with AR collapsable stock, side saddle, SureFire forend, and a single point sling.