Colin Furze is a popular and probably insane inventor who regularly builds things on a scale that not many makers are capable of. Every once in a while, his projects involve airsoft replicas in some way or another.
In this project, he builds a machine gun hidden inside a briefcase. In doing so, he shows a plethora of automation mechanisms useful for any sentry build.
First, he uses a gear with some teeth removed (much like the actual internals of a gearbox) to load the shots. Then a linear actuator and a lever to pull the trigger. The whole operation is controlled with an electronic board containing relays and an antenna. The user can either shoot with a button in the handle or with a remote control.