Ro-bert
It replaces the standard top cover. There are seven screws to clamp it to the upper, which do NOT mark the rifle (it clamps on the inside of the top cover slide channel). There is also an adjustable recoil stop at the top rear. It is as rigid as it can ever be, given the design of the rifle.
I have not shot mine with the scope/mount yet, it is out for its first time next Saturday