ANY modification to ANY serial # on the main frame can not be modified. SteelSlaver's mod is a direct violation because his 'slicing & welding' method (in ATF's eyes) can be looked upon as a 'switched serial #' from one frame to another, even if any other markings match because the original IS the main one on the butt of the frame. The other markings are considered secondary. You can not alter a frame from it's original mfg configuration in any way. Even if filing a SB to a RB that doesn't come close to the #, is still a violation. Just don't do it. Live with it and buy a RB in that model.