When S&W first come out with the original 357 magnum, it was an N frame and a special order gun. Each was assembled and fitted by their top craftsmen to buyers specifications as to barrel length,range sighted to at factory etc. In addition t a serial number each had its own registration number stamped in yoke cut out. Paperwork was provided for owner to register gun with factory after delivery. The holy grail of most S&W collectors. Its was later produced without registration number, then evolved into the pre model 27 then the model 27