Hi Quada. For the older rifles (pre WWII), I think it was around the early to mid 1930s when Marlin stopped using octagon barrels. I have a Model 93 short rifle in 30-30 cal with 20" octagon barrel from that period. It has a crescent buttplate too. Also have a 1941 made Model 1936 in 30-30 cal. Both have case colored receivers which I agree look really nice on these guns. Not sure what years the 38-55 cal was offered.