Book excerpt: This manual provides operation and maintenance instructions for the M16A2, M16A3, M16A4 Rifles, M4 and M4A1 Carbines. These weapons are lightweight, gas-operated, air-cooled, magazine-fed. shoulder-fired weapons that can be fired in either automatic, three-round bursts, or semiautomatic. The purpose of the weapons is to provide personnel an offensive/defensive capability to engage targets in the field. The adapter rails allows the operator the capability to mount various accessories on to the M16A4 Riffle and the M4/M4A1 Carbines. When a procedure is common to M16 rifle and M4 Carbine, ONLY the M16A2 configuration will be depicted. If a procedure is not common to both -weapons, the procedure will be incorporated and the weapon will be identified. If your weapon is configured with adapter rails, refer to the appropriate appendices in this manual for operation and maintenance procedures for the adapter rails.