https://www.cdnnsports.com/smith-wes...l#.WjRaud-nHIU
This isn't the "sport" model, it's the M&P15 with the M4 barrel profile. I called CDNN and they said the quad rail is factory. I went ahead and ordered one, but it'll probably be after Christmas before I can get back to the FFL to pick it up.
$499.99.