Sebus Airsoft outlines the first prototype of 3D Printed Gas Blowback Airsoft gun design, requiring several components for assembly and function. You'll need an airsoft MP5 magazine, a standard M4 hop-up and barrel (length is customizable), a common compressed air pistol, and a HPA tank or other compressed air source. Additionally, gather two M3x15 screws, a very light main spring (minimum 20mm diameter, 100mm long), a nut to add weight to the bolt (for which a slot is provided), and a single airsoft BB for the nozzle valve. The replica operates at a minimum pressure of 6-8 bars. For 3D printing components, use a 99% infill and tree supports.