Zombie Cliché Lookout:

The thing about zombies is that if there are only a couple of them, and if you’re reasonably well armed (carrying a loaded Glock, for example), then they’re just not as scary. So what does the aspiring zombie writer do to up the ante? Gun jams, broken weapons, loss of ammo, mobs of the undead. If you can think up a way to cheaply stack the odds against the protagonist, zombie stories will do it. That is, of course, until it’s time for our heroes to start kicking wholesale ass, at which point all bets are off.