ISMI Premium Extra Power Firing Pin Spring prevents the firing pin from striking the primer when the slide is closed. The heavier spring keeps the firing pin stop from dropping out during firing. All ISMI Springs are made from silicone chrome instead of 150 year old music wire. Every ISMI spring is heat treated, shot peened & stress relieved to enhance durability, consistency and reliability. ISMI is a contractor of the U.S. government and produces springs used in machine guns with incredibly high cycling rates. Also, the creator of ISMI springs obtained his knowledge from extensive research in the development of springs used in Indy car racing.