Just FYI, firestorm's glitch isn't limited to only the faster shooting opinion. You can also increase the range of your Tack Shooter to the point where it can cover the whole screen. As if this hard badge wasn't easy enough. -_-
I'm pretty sure I just spend 2 hours failing at Bonus level 5: The Killing Floor before I realized the Hard achievement asked for six finished Bonus levels and not ALL seven.
Wish I noticed it earlier! D=
I went out of my way to make sure I didn't shoot my zombie girlfriend only to read the comments after I finished that she's some bullet-immune zombie ghost. >.<