Thanks for the info, Goony. I just held the serial number area of the butt under a bright light. I can faintly see the area where the swivel hole has been filled in. It is not noticeable at all unless looking under bright light. No grind marks or discoloration to the finish, etc. With the grips removed, I just noticed the swivel pin is still in the frame. Do you think the "fill-in" was done at the factory, or by an Army armorer? Skip48