Gundam fans might want to take a look at this project. The Zaku Machine gun gets replicated and it's a working, shell-ejecting model with fire modes from single, 2-round, 3-round, 4-round, to full auto and the Pan magazine also works. I cannot confirm if this is an airsoft one or more of a cap gun-type since it shows some smoke when fired.

But what got me interested is at the beginning of the video in which an airsoft gun with a pan magazine actually works.

Thanks to Public Enemy for this.