ok.. i found it in the FAQ things..
"Q: What shotguns will it fit?
A: The SpecOps NRS is available for RemingtonĀ® 12 and 20 gauge 870 Series pump shotguns along with the 7615, 7400, 7500, 7600, 740, 750 and 760 series rifles; and all 12 and 20 gauge MossbergĀ® 500, 590, 835 variants, and Maverick 88 models. The SpecOps NRS is not compatible with semi-automatic shotguns."