03-11-2016, 11:50 PM
I have never, ever worried about this, but I can get 0.023" worth of feeler guage to slide between the rails on the handguard and the receiver. My thought is to get the rails as mutually level as possible by clamping a scope ring right on transition and then let the mounting screws and lugs on the handguard "float" it into place fore and aft. I don't see any reason to get it flush against the receiver.