Loyalist:
rglenz has correctly identified this rifle as a rare small ring Rigby Pre-98 "Transition" Sporter. The 222.5 barrel marking indicates a .275 cal. (7x57). The mismatched bottom metal would explain the lack of a Rigby S/N on the trigger guard. I also notice a misaligned witness mark on receiver/barrel. Is there a S/N on the bolt handle root and inside the stock receiver channel ? A chamber cast is recommended to confirm any other modifications. I doubt that it is a 303 which required a slant magazine and was brought to market at a later date.