I have looked all over the web...I Think it might be a 1903 2nd change. I has 4 screws and the S&W trade mark on the passenger (right) side. I think it possibly has internal hammer block. The frame and barrel and cylinder have the same #'s 3369xx...the crane and where the crane meets the frame are stamped 314xx...drivers (left) side of the barrel has 32 winchester ctg ...top of barrel has Smith & Wesson springfield mass u.s.a. and a series of pat'd dates starting with apr 9 89....and ending with july 7 03. the barrel bore has a twist pattern inside, rifleing ?? I think it's called.