What is the rail on the bottom of the stock called and who makes a good Picatinny adapter for it? I want to use a LaRue picatinny quick disconnect attached to a Harris bipod. I tried a Shooters Ridge swivel stud picatinny adapter but it's apparently not to spec because the LaRue is loose on it. I know the Larue is good because it fits tightly on my centurion C4 rail. Any help would be greatly appreciated. PS- that's not my stock, just a google image.