best gun for killing zombies

[OVERKILL]

 You wouldn't have any links to lend credence to the 22 bouncing off the skull statement would you? Not that I doubt it, I remember seeing something called the "skin, skull, brain model" where a group at a university had developed a very realistic replica of the human skull and were able to duplicate wounds on the model very similar to those caused to humans with the same rounds. I remember they stated that 22 long rifle and 9mm (probably 9mm Parabellum) were used and there were pictures of simulated wounds where the 9mm had bounced off the simulated skull on glancing shots. The velocity, bullet weight, bullet construction nor shooting angle were not listed. I was hoping you may have better information as to specific circumstances.

[Labdwakin]

With Zach... we're looking for either enough penetration or enough impact trauma to sever the spinal cord. If you look at this cutaway of the human skull, you can see how small the target area is for a bullet of minimal penetration from the front.  A 45 ACP 230 grn bullet has the same energy in the impact as a 93 mph fastball but concentrated into an area less than half an inch across.  Add to that the well known cases of misfires en-masse of 22 LR ammo and I would rather just prepare with the 45 and if I have to go to a 22 eventually, I will.

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[Slinger]

I have to agree with the .22LR...  to an extent:

As Pulseofthe Maggots said, they are accurate, and the lightweight rounds allow more ammo to be carried.

Also, think about this:  if on the move (city or country) you have to eat.  You can't carry enough rations to last too long of a while, and would you stake your life on being able to scavenge from stores and homes?  The .22LR has been used to bring down game from moose to rat for a very long time (although I would stick to rabbit or cat or something smaller, imagine trying to harvest a moose or even a deer with a .22, though it has been done, and often). Of course, if you're vegetarian that isn't a factor.  And I didn't mean to offend anyone with the cat part, but they are made of meat.  Don't think I go around killing cats or anything, and eat them, because I don't.           
Yet.

Having said that, I think I would want something with more stopping power.  After all, its not just zombies you'd have to worry about, but normal human looters and bandits as well.

As for myself, I have to go with my Marlin 336 R.C.  .30-30, lever-action.

Light.  Slim.  Beautiful.  My baby...

Plus, a thirty caliber bullet is a man-stopper, most likely an effective zombie-stopper, too.

Now my basic "bug-out" package (I don't aim to bug out, but what else would you call it? besides, you never know) also includes my S&W .41 magnum revolver.  They make a lever-action carbine chambered in .41 mag (just like they do for the other big pistol calibers, .357 mag, .44 mag, etc.) but they're hard to find and I imagine they're pretty proud of 'em (i.e.  expensive) but that would be sweet, both weapons using one ammo.

[OVERKILL]

 That's agood point about the stray cats. A lot of animals that no one generally would eat now may end up on the menu if you want to stay alive. Cats, dogs, rats, horses all kinds of bugs and insects. Lizards.

  I'm still of the opinion that while a 22LR has  place in every battery, it wouldn't be my main gun. Maybe as a sidearm to back up a light carbine.