Nerf gun! - Fully 3D-Printed (almost)

https://youtu.be/BiFoJVlH2Q8

This design is almost entirely 3D printable, requiring only some rubber bands and a 20 mm by 2 mm O-ring—or you can opt for a tight-fitting piston head (Choose from the different sizes depending on your 3D printer) with a good slather of Vaseline for similar performance. Capable of shooting Nerf darts over 30 feet, this toy gun offers customizable firepower based on your choice of seal and the number of rubber bands.
Remember: safety first! Never aim at eyes or faces.
For the trigger hinge use a piece of 1.75 mm filament.
You can find 3D files and more details here-