ProMag Roller Follower Polymer AR-15 5.56mm Rifle Magazine 40 Round OD. It is constructed of DuPont Zytel polymer with an anti-tilt roller follower and mag spring formed from chrome silicone wire. Specifications for ProMag Roller Follower AR-15 5.56mm 40 Round Rifle Magazine: Manufacturer: ProMag Fabric/Material: Polymer Magazine Capacity: 40 Round Caliber: 5.56x45mm NATO Gun Make: AR Platform Gun Model: AR-15 Package Contents: ProMag Roller Follower AR-15 5.56mm 40 Round Rifle Magazine What firearm models does the manufacturer say ProMag Roller Follower AR-15 5.56mm 40 Round Rifle Magazine is compatible with? The manufacturer suggests that ProMag Roller Follower AR-15 5.56mm 40 Round Rifle Magazine is compatible with AR-15ProMag RM-40-OD: Roller Follower Polymer AR-15 5.56mm Rifle Magazine 40 Round OD