ATI has developed an adaptor which allows you to mount any AR-15 stock on popular 12-gauge pump shotguns. The ATI Talon Tactical Shotgun Stock System is available for the Mossberg 500/535/590/835/Maverick 88, Remington 870, and Winchester 1200/1300 models, includes a pistol grip and retails for an MSRP of $44.99. Packages including a 6-position adjustable stock has an MSRP of $134.99.

From the press release:

New for 2011 are the ATI Talon Tactical Shotgun Stocks with the New Triton Mount System and Scorpion Recoil System. The Talon Tactical Stocks feature the new ATI Triton Mount System. This system allows tactical changes for whatever the situation demands, from breaching doors to tactical close quarter responses. The Triton Mount System is CNC Machined from Military Grade 6061 T6 Aluminum. The Mounting System features an angled, self-aligning dovetail locking system for easy, secure installation. The Triton mount System allows the user the ability to switch from a Six Position Collapsible stock, to a Rear Pistol Grip in a matter of seconds. The Triton Mount System also includes interchangeable sling mounts for left and right-handed shooters, and an additional blank spacer for when a sling mount is not in use.