Quote: Very special, very early 98 action you have there! I would think the floor plate is a replacement, Rigby put their number on the trigger guard. If still the original chamber,_ sure it's a .275.
Unfortunately there is no marking on the trigger guard - which is why I was led to think that the serial number is the one on the floor plate but you are likely correct! Would Rigby have stamped any other parts with their serial?