This is a video of backyard survivalist Joerg Sprave demonstrating the fully automatic crossbow he built using wood, giant rubber bands, and a cordless drill. It works unsurprisingly well, because Joerg's weapons almost always work flawlessly, despite their complication. This guy should work for NASA or Home Depot. Obviously, I'm gonna need him in my crew if I expect to survive the zombie apocalypse. Now -- and I'm just throwing this out there, but I think wearing me on his back like a backpack is probably best.
Keep going for the video.
Thanks to Matt D, who agrees being able to make your own weapons is going to be key once all the guns and ammo shops have been looted following the appearance of the first zombies.