ProMag magazines are designed utilizing both traditional stamping and welding of heat-treated high carbon steel, and modern precision injection molding of mil-spec polymer compounds. Every ProMag magazine is backed by a lifetime guarantee against manufacturers defects. Made in USA. Drum housing constructed of a proprietary DuPont Zytel based polymer Magazine upper tower has full length steel internal insert stamped and welded like the factory magazine Injection molded magazine follower Magazine spring formed from heat treated stainless steel Made in USA