How can you find out how old your smith and Wesson handgun is?

A Smith and Wesson model 66 stainless steel 4" barrell with no dash after the serial number is one of the earliest year guns. It should have all stainless metal with stainless sights front and rear. Black sights or orange inleted front sight is newer model. A no dash with orginal stocks in very good condition can go between 450 to 850 dollars depending on condition of workings and finish. Stock condition has little effect on value.