OK, everybody knows I am not an expert on SA's, however, the 1798 number is all on the same plane with the same size numbers which would tell me it was probably roll stamped not hand stamped. That said, the 4 underneath is a "skinny" number and didn't they use that type of stamp for very first production and prototypes and such? Just asking. Could it have been a very early frame (only) and was then used to make a complete production revolver? I haven't had a chance to get into any of my Ruger books to look at/research things (getting my stuff together for Tulsa).