I don't play HvZ (Humans versus Zombies, for those of you that aren't up to date) since I'm a grad student. Read that as: I live in my lab, they'd never tag me. However, if I thought I'd be able to play fairly, this would be my weapon of choice.
That is a working Halo Assault Rifle made to shoot Nerf darts at people.
You can see the artist's post on his glorious weapon
here....