You have a S&W 32-20 M&P, pre war, K frame revolver. S&W discontinued 32-20 K frames before WWII. The 32-20 is also known as the 32 WCF (Winchester Center-Fire) or the 32 Winchester, which are all the same cartridge.
With the SN you provide, the subvartian is specifically a 1905 4th change. If it has an adjustable rear sight, then its a target version, which are pretty scarce. The gun likely shipped out in the 1930s, but if earlier, I would say late 1920s. These were slow sellers, and often sold and shipped much later than the SN would have you believe.
They are better in nickel, but if factory nickel it should have a case hardened hammer and trigger, IE they should not be nickel plated. A quick way to check is to open the cylinder, flip the gun over, and check the barrel flat. The SN should be there. If there is no letter "B", then it likely shipped as a nickel gun. IF there is a "B" prefix, then that part was slated to be blued, meaning that the entire gun was blued. Of course however, even if the "B" is missing, indicating nickel, it could have been refinished in nickel. Pics would help determine originality. The SN should be found on the rear cylinder face, the yoke (swing out arm, in front of cylinder), bottom of barrel, frame, and right grip panel.
