During WWII their code was byf in small letters. I had a very nice byf 41 that I had barreled to 257Robts and a nice checkered bolt handle installed. Barrel was a Pfieffer which was a premium at the time which was 1952. I carried the barreled action to gunsmith school with every intention of finishing it. Traded it almost immediately for a 257AI custom by one of the students. It was a super clean action.