No disrespect to Mr. Flayderman, but it is the last place I would look for help in properly identifying any gun. Buy the Neal & Jinks Smith & Wesson book. The 38 Single Action revolver was made from 1877 to 1891 in serial number range from 1 - 108,255. A change to the extractor catch was made with the 1880 patent and when that change was made, the factory discontinued the 1875 patent and added the 1880 patent. That should have applied above the 50,000 serial number.
Your revolver has had a couple of alterations made to it. First, the stocks are not original and may have been handmade. Second, is what looks like a rivet has been placed as a barrel pivot pin. What does the other end of the pin look like?