The Classic M16A2 upper receiver is a fixed carry handle receiver which accepts the adjustable drum sight. In order to build a M16A2 clone, you will need either the stripped upper receiver, or the pre-assembled upper receiver. If you buy a stripped upper, you will need an A2 upper receiver parts kit which will include the rear sight drum. The Classic M16A2 upper receiver is a fixed carry handle receiver which accepts the adjustable drum sight. In order to build a M16A2 clone, you will need either the stripped upper receiver, or the pre-assembled upper receiver. If you buy a stripped upper, you will need an A2 upper receiver parts kit which will include the rear sight drum.