Sorry if I published it again I'm not sure if I published it the first time
Use a air compressor
Select as Best AnswerUndo Best Answer
im coming up with one but its not "mini" its a bit bigger :-(
check out my instuctable
If it means small, this won't work, but anyway...https://www.instructables.com/id/Ultimate_Bic_Airsoft_Gun/
It would be hard to do because the amount of ammo needed for automatic fire would not fit in a pen.