The BCA forged standard charging Receiver/BCG combo fits any Mil-spec lower receiver. This combo includes a BCA standard charging BCG, charging handle, and the BCA Forged upper receiver. This combo is perfect for a bolt action/Semi auto build or perfect for an ergonomic and unique work horse build. Specs: M4 Flat Top Forged Upper Receiver w/ Forward Assist Standard Charging Made from 7075 Aircraft Aluminum BCA Bolt Carrier Group 6.5 Grendel Type II and 6mm Arc Caliber Anodized Black