Sig Sauer E300A120: The Sig Sauer 300 Blackout Match Grade Centerfire Rifle Ammo is designed to bring out the best in today\'s high-performance AR rifles. The ammo features match grade brass cases and will run through standard 223 Remington/5.56mm NATO components including magazines. These Supersonic rounds feature Sierra Matchking projectiles for superior accuracy, increased downrange terminal performance, and low noise level characteristics.