+3 BRT M4A1 Bolt Carrier Group C158 HPT/MPI Auto SKU BCG-M4A1 $169.00 In stock Quantity: 1 Add to Bag Product Details Full auto bolt carrier for the AR Family of Weapons (AR15, M16, M4) 100% made in USA to current USGI M4A1 specifications. The USGI full auto bolt carrier is Manganese Phosphate coated outside and Hard Chrome lined inside. The Mil-Spec gas key is chrome lined and secured with properly staked Grade 8 fasteners to ensure reliable gas system performance. Carpenter 158 bolt is shot peened, HP tested and MP inspected. Save this product for later Favorite