The magazine body is constructed of heat-treated steel with a black oxide finish for durability and harsh use in the field. A chrome-silicon wire spring and precision-molded polymer follower ensure reliable feeding and function. This magazine is for AR-15 rifles chambered in .223 Remingtonl/5.56 NATO.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 a black oxide finish Injection molded magazine follower Magazine spring formed from heat treated chrome silicone wire This 5 round magazine is the length of a G.I. 20 round magazine Made in USA