The standard long action hammer goes back to the beginning of production. The switch to the short action high speed hammer began around mid-1948. It is sometimes informally called the "fish hook" hammer. I believe it was used until around the time model numbering began in the late 1950s, when the hammer spur was changed to the semi-target style. There is no such thing as a "transition" hammer. In fact, I wish we could just scratch "transition" from the S&W lexicon permanently. It causes more confusion than it is worth.