Buy Smith & Wesson M&P340 357 Magnum J-Frame Revolver with Night Sight Online. Smith & Wesson’s unique Scandium Alloy high strength frames allow for the lightest revolvers capable of firing .357 S&W Magnum®, or .44 Magnum. The Smith & Wesson J-Frame has become the most popular small frame personal defense revolver on the market. With decades of reliable performance to its credit, the J-frame line offers models capable of firing .22 LR, .22 Magnum®, .38 S&W Special and the more powerful .357 Magnum® loads. Smith & Wesson offers these revolvers from their production, M&P, Pro Series, and Classics lines in three diverse hammer designs; internal, exposed and shrouded.