There's nothing to try. If you don't have the right tube it's not going to work. You can check the diameter of your tube. Quote from GH's site " This version clamps to pistol buffer tubes or adapter spuds ranging from 1.17″ to 1.2″ in diameter"
My tools and tape are in my job trailer. Of all the weekends to not bring my tools home with me, lol. So I'm looking on RRA website, and they're not listing a diameter for their tubes. Are you familiar enough with Rock River to know off-hand if that brace will work?