Still thinking of getting the Tippmann M4 HPA-powered Airsoft Rifle? Doctor Milsim can help you in making that purchasing decision by showing you internals and improving performance.. This is an interactive video and you can select which portion to watch... "Explore the Tippmann Airsoft M4 GBBR internals in greater detail. See how it breaks down, what the internals look like, and how to tune it for silky smooth performance!