a competent laser engraving company should be able to fix the engraving by going deeper. I would let them fix it and if they do mess up (which I am doubtful they would) go back to you dealer and let him know you need 3 new rifles + 600$. You could double engrave but that is not aesthetically pleasing but up to you. The atf ruling is clear
7.4.1 Serial numbers. Each manufacturer of a firearm must legibly identify it by engraving, stamping (impressing), or otherwise conspicuously placing on the firearm’s frame or receiver an individual serial number not duplicating any serial number placed by the manufacturer on any other firearm.120 The requirement that the marking be “conspicuously” placed on the firearm means that the marking must be wholly unobstructed from plain view. For firearms manufactured on or after January 30, 2002, the serial number must be to a minimum depth of .003 inch and in a print size no smaller than 1/16 inch.
7.4.1 Serial numbers. Each manufacturer of a firearm must legibly identify it by engraving, stamping (impressing), or otherwise conspicuously placing on the firearm’s frame or receiver an individual serial number not duplicating any serial number placed by the manufacturer on any other firearm.120 The requirement that the marking be “conspicuously” placed on the firearm means that the marking must be wholly unobstructed from plain view. For firearms manufactured on or after January 30, 2002, the serial number must be to a minimum depth of .003 inch and in a print size no smaller than 1/16 inch.