Why use a Magpul PMAG 30 AR 300 B Gen M3 Mag when a standard AR mag will work with your 300 BLK ammo? It's all about the stack. This specially designed 300 BLK Mag eliminates 5.56 mag control points that don't interface correctly with 300 BLK ammo. That means you get a proper stack, with ammo feeding correctly with little side pressure and less friction for more reliable shooting than you would experience with a 5.56 mag. And it doesn't limit the capacity of your Mag, which can happen when loading 300 BLK into a 5.56 mag. You'll fit 30 rounds of 300 BLK in these mags, and you'll enjoy flawless shooting, too. Fits AR-15 and M4 platforms chambered in .300 AAC Blackout Optimized internal geometry accommodates the wide variety of bullet profiles used in .300 BLK cartridges Reinforced all-polymer construction Anti-tilt, self-lubricating polymer follower reduces friction, increases reliability Constant-curve body for smooth feeding Easy to disassemble slim floor plate Long-life stainless steel spring Distinct rib design and upper-half texture provide a distinct visual and tactile difference Paint pen dot matrix panels on the bottom of the body for identification marking Note: Dust cover not included, sold separately Order today!