ProMag's Rollermag reinvents the wheel by adding them to an anti-tilt follower, in a Technapolymer magazine body. Experience a smooth, anti-tilt rolling feed with the revolutionary RollerFollower for maximum friction reduction. The magazine is built with ProMag's anti-fatigue chrome silicon springs, so you can keep them loaded and stashed for up to six years without worry. This model has a 15-round 223 Rem/5.56 NATO capacity.ProMag magazines are designed utilizing modern precision injection molding of Mil-Spec polymer compounds. Every ProMag magazine is backed by a lifetime guarantee against manufacturer's defects. Features: Magazine body constructed of a proprietary DuPont Zytel based polymer Patented anti-tilt Roller follower Magazine spring formed from heat treated chrome silicone wire Made in USA