I cannot identify this 4.5" barrel for the Model 41, unsure if it's factory, stamped S&W .22 long rifle or something I cannot identify, only seen one other in a picture like it, I've had this pistol with the 5.5 & the extra 4.5" for years, Ser# A225XXX, finally pulled it out & know I'm trying to figure out what I really have? Help--- Barrel is slimmer, different rear sight, both the 5.5 & 4.5 easily attach to the frame with no problems. Is this barrel the hunter they call the lightened 5" barrel??