I am probably the least qualified to respond, but If you open the cylinder you should see a something like MOD. then a number right above the hinge. That will help. But if I had to guess from the picture I would say it looks like a model 10. If you look on the bottom of the grip frame you will see the serial number. If you post that number and letter(s) someone can tell you the approximate date your gun was shipped from Smith and Wesson.

Wingmaster