Um. Wow. It’s attributed to MOCPages member PLUM B, and here described by The Brothers Brick:
[F]eatures a clip-fed firing mechanism that shoots rubber bands – perfect for taking out the paper Locust horde. If that’s not enough, the saw blade on the front of the gun is motorized for slice and dice action.
[via Boing Boing]
I’d call the chainsaw underwhelming… compared to that awsome clip mechanism!
Still a really cool prop overall, and well explained.