Sig Sauer E300A220: 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 Subsonic rounds are ideal for suppressed AR rifles. They feature Sierra Matchking projectiles for superior accuracy, increased downrange terminal performance, and low noise level characteristics.