The model 12 air weight M&P is a unique revolver. The Standard Catalog of S&W doesn't’ specify the number made, but it does so NOT to shoot the ones that have an alloy cylinder. The 6” barrel was added in 1959 and deleted in 1960, so it is a rare bird. As usual, pictures help immensely as well as serial numbers. The book says the model 12 was numbered with the 10, 11, 45, and the Aircrewman.