That's a nice transitional OD! The only thing that would make me think it might be a re-barrel is the "corrosion" where the front sight ramp meets the barrel rib. I've only seen this condition on later (early 1950s) N-frame revolvers like my first year Highway Patrolman. It's been blamed on the bluing salts that S&W used at the time. It could be that those same bluing salts were used in the late 1940s. Your revolver has some interesting things...like the hole drilled in the hammer (for lightening?). I also see something going on in the cylinder holes that almost looks like cracking or peeling and doesn't look like leading. I've never seen that before. Regardless, it's a fine revolver. Enjoy!