Is there a year marked on the barrel at all? I have a 'BSA & Co' marked MLE in Range Pattern configuration with a '20 dated barrel. It has the matching 'PB' prefix serial number on bolt, reciever and barrel (pretty rare in NZicon to have a MLE with matching numbers). Apparently NZ aquired the remaining stocks of MLE parts from BSA in 1920 for refurbishment of is MLE rifles so perhaps your action is from that period?