I agree with Al. It is likely that S&W was still using up older frames that were made before the "10" stamping was used. The production date of your gun occured just when these changes were being made.
You can write S&W and for a $30.00 charge their Historian, Roy Jinks, will research your particular revolver and reply with a factory letter with all of the details their records show. This is the only way to know exactly what you have.
Given the information I now have I would describe your gun as a:
Smith & Wesson 1905 Hand Ejector/Military & Police (Postwar) Pre-Model 10. Date of production is between 1957-1959 with the later date being most likely.
Understand that S&W would make large production runs of frames, serial number them, but not actually build them up into guns until sometime later.