Abstract: An apparatus and method for heating the elongated, generally cylindrical surface of the internal elongated bore of a gun barrel preparatory to quench hardening of the cylindrical surface. There is provided a generally cylindrical inductor extending through the gun bore with electrical connector means between the gun bore and inductor at each end. One of the electrical connecting means includes an electrical circuit between the barrel and inductor wherein the electrical circuit includes means for creating a high frequency alternating current flow in the path including the inductor and gun barrel, in electrical series, whereby heating of the gun barrel is concentrated adjacent the cylindrical surface of the bore.