T-N.T. Studio APS-X HOP-UP System H+ Retrofit Kit for GHK M4 GBB (455mm)

T-N.T. Studio APS-X HOP-UP System H+ Retrofit Kit for GHK M4 GBB (455mm) Metal Construction Include HOP-UP chamber & Inner Barrel better air-tightness, BBs feeding more smoothly!! No more jam!! No more BB broken!! and do not choose BB type ANYMORE! Suitable for GHK M4 Series Airsoft Gas Blow Back GBB Rifle