This replacement magazine for your Smith & Wesson Shield is constructed from heat-treated blued-steel. Its components molded from a proprietary Technapolymer and anti-fatigue spring, so you can keep the magazine loaded and ready for up to six years without concern.ProMag magazines are designed utilizing traditional stamping and welding of heat-treated high carbon steel. Every ProMag magazine is backed by a lifetime guarantee against manufacturer's defects. Features: Magazine body constructed of heat treated carbon steel with black oxide finish Injection molded magazine follower Magazine spring formed from heat treated chrome silicone wire Made in USA