OP, look at the Knoxx/Blackhawk SPec-Ops stock, or the Mesa Tactical adapters with the Endine buffer installed. The Knoxx stock isn't cheap at $100 or so, and the Mesa is even LESS cheap, but either one can be a great way to reduce felt recoil. The down side is that a pistol-grip stock makes it somewhat more difficult to use the controls (safety and bolt release) on the 500 series Mossbergs.
Never argue with an idiot. They will drag you down to their level and beat you with experience.