Smith & Wesson Model 640, Classic, Engraved, Double Action Only, Metal Frame Revolver, J-Frame, 357 Magnum, 2.125 Barrel, Stainless Steel, Matte Silver Finish, Wood Grips, Fixed Sights, 5 Rounds 150784 Based on Model 40 Centennial, the Model 640 is a small frame concealed hammer revolver that packs a full-sized punch. Beautifully enhanced with diamond-tipped machine tool scroll engravings on the frame and cylinder, the Model 640 integrates the time-tested features of the original with modern advancements.