This is a 3D printed remix of RBguns' Stepup action rubber band gun. His video can be found on https://www.youtube.com/watch?v=NLb-8ofC3Zk
Trigger mechanism has been simplified.
Trigger springs forward naturally by the tension of the ammunition. Trigger won't return when gun is empty. Time to reload.
This is a small gun so it won't hurt little kids. Just be careful not to hit eyes! Scale up for big boys.
Insert trigger into main body. Make sure it glides smoothly. Try with cover on. Sand if necessary.
Glue cover on and underbarrel.
Feel free to modify or remix the model > https://www.tinkercad.com/things/8AiODbNQrNw