A metallic liner for a composite reinforced high pressure gas cylinder is composed of a seamless metal tube contoured with a top dome and bottom dome. The liner is further composed of a seamless top metal end cap having a mating shape of the top dome and a seamless bottom metal end cap having a mating shape of the bottom dome. Alternatively, an extruded cup is shaped to a dome at the open end and one or two seamless metal end caps are used. In the method of manufacturing, the top and bottom ends of the metal tube are contoured, the end caps are produced, and one or two end caps are attached to the ends of the tube.