The numeral "1" stamped on the underside of the receiver is actually the letter "L", which was sometimes used to designate actions to be used for 256N or 30 USG cartridges. The receivers destined to be 30/35 N were stamped 30 C. There seemed to be no hard and fast rule which ones were stamped or not stamped, but the L stamping is far less commonly encountered, in my experience.