I have a 3.75" rail installed under the forearm. It was a very simple affair (which is about all I can handle!)... I drilled two holes in the stock for the screws. You can't see it in the last photo, but I did use a Dremel to inlet the inside of the stock just enough for the top of the screws to fit flush with the stock material. Tighten the screws just "snug" so you don't crack the stock. Make sure to use some Blue Loc-Tite on the screws and it'll be rock solid. BTW, I set it as far aft as I dared while keeping it (reasonably) horizontal - the stcok curvature will angle it upwards if it's too far back.