I designed this for my Nerf Face Tracking Turret project on youtube.
It fits these Servos: https://www.amazon.com/gp/product/B07GRMRH1Q/ref=ppx_yo_dt_b_asin_title_o00_s00?ie=UTF8&psc=1
The barrel receives a 1/8" vinyl tube for air supply on one end, and a nerf dart fits over the other end