Welcome to the forum. My copy of the RENE Reference places your serial number in 1972 and says you have a model BKH-44X. Production started in 1971 and ended in 1973 when the transfer bar safety system was incorporated in the design and the New Models appeared. No actual production numbers are known (typical of most Ruger products) but the RENE Reference does have this to say: 'BKH-44X and BKH-45X with silver eagle medallions. Known s/n range 45-07574 to 45-23016. Only a few thousand of each produced with the BKX-44X being the scarcest.' I think it would be safe to say you have a 'scarce' old model Blackhawk.