GSI Hop-up Arm for APFG (MCX / MPX)GSI Hop up arm for APFG MCX, increases accuracy (hop up tensioner included) The hop up arm included as standard in the APFG MCX series has a lot of left right play, which makes bullets not come out consistently. To solve this problem, GSI improved the play of the hop up arm for the MCX and matched it with a dedicated hop up rubber and hop up tensioner to create the optimal bullet collection. This precision engineered upgrade ensures your shots are