The state of the art M4E1 platform starts with the M4E1 Upper Receiver. The M4E1 upper receiver is a one-piece design combining the handguard mounting platform with the upper itself. Since the rail mounting surface and upper are of the same forging, not only is it a stronger system, but it also provides for easy installation of the gas tube with a pre-aligned gas tube hole. Additional lightening cuts save weight and allow for more efficient cooling.