I don't know ... my weapon-of-choice is a shotgun.
Nah, against Zombies you need a head-shot. A shotgun while spreading lots of buckshot (or quarters) around, doesn't focus on the area that needs to be hit.
A .22 holds 15 Long Rifle or 22 Shorts, but I'd be looking for the Ruger 10-22 with the round magazine. Low recoil, low noise (comparitively speaking), and I'm not a bad shot. Plus the ammo is small, light and cheap.