A 300 Blackout BCG (bolt carrier group) is a key component for AR-15 rifles chambered in 300 AAC Blackout. It includes the bolt, carrier, gas key, firing pin, cam pin, and retaining pin. The 300 Blackout BCG works with AR-15 upper receivers, 300 Blackout barrels, charging handles, and lower receivers. It ensures reliable cycling, chambering, extraction, and firing, making it essential for building or upgrading AR-15 platforms in 300 AAC Blackout caliber.