The Tapp M4 Modular Adapter converts your traditional gas airsoft gun to use HPA and accept standard M4 AEG magazines (super-feed mags recommended).
Modular design allows lower to be changed to different lowers. This makes the adapter interchangeable between M4, ARP, Shotgun Shell, etc. (Lowers can be found here)
Friction-less BB stop allows smoother feeding and prevents BB loss while reloading.