AR-15 BOLT CARRIER GROUP The L7D3 is the perfect BCG for a Mil-Spec build or upgrade from sub-par equipment. LMT Defense has made the full-auto M16/M4 BCG and its components for years replacement parts for the United States hard work war fighters and other that need reliable equipment. These BCG's are standard equipment in all of our complete full auto weapon systems. Works well with both suppressed and unsuppressed weapon systems. Also available in L7A3 Semi-Auto Only. Mfg: Lmt Defense