ProMag RM-40-SL Magazine for AR-15 5.56mm 40 RDs Features: Made in the USA the AR-15 steel lined magazine features a patented anti-tilt roller follower. The mag is constructed of DuPont Zytel polymer with a stamped steel feed lips mag catch and heat-treated chrome silicon wire. ProMag RM-40-SL Magazine for AR-15 5.56mm 40 RDs Specifications: Caliber : 5.56 NATO Capacity : 40 Finish : Black Model : AR-15 Material : Polymer Model Fit : AR-15