but if your dealing with end of the world zombies, you'll want to keep your hearing so you can hear them a sneaking up! plus a loud shot would attract more.
Here's my choice for the zombie hoardes(sorry my post-fu isn't strong enough to post the picture).
It's the PMR-30 from Kel-Tec. .22 WMR with a 30 round internal grip magazine. Even with the always advisable "double tap" to the head, it will drop them in droves. It will hopefully be releasing this month, but demand is expected to be high. Should sell for around 350 to 400.