Smith & Wesson J-Frame revolvers have had your back since 1950. These small revolvers were designed to fire a full power round and are as simple and easy to use as they are reliable. Available in various calibers and with three diverse hammer designs, it is no surprise that the Smith & Wesson J-Frame has become the most popular, small-frame, defense revolver on the market. The Model 640, is a variation of the Model 40 Centennial that integrates the time-tested features of the original with modern advancements. The Model 640 is a small-frame, concealed-hammer revolver that packs a full-sized punch.