ponder me this: zombies vs guns

Watching The Walking Dead can make anyone start pondering the Zombie Apocalypse and the logistics of surviving ... here's one of many conversations Lou and I have had about such a topic.

cpg - "Can a .22 to the head kill a zombie?"
lag - "Yeah."
cpg - "We should be stocking up on that."
lag - "Well, yeah ... but - let's say that you and I were the only ones left in the world, everyone else were zombies. That's 6 billion zombies to get rid of - 6 billion rounds of ammo. The barrel on the gun only lasts 5,000 rounds. Even if you use each barrel twice as long as you normally would - so 10,000 rounds ... that's 600,000 barrels."
cpg - "Huh, I see. Sooooo, you're saying we need more guns."
lag - "Welllllllllll ...."

here comes a bunch of math ... 
500 rounds of .22 ammo takes up 41.50 cubic inches.
We need 12,000,000 boxes of 500 rounds of .22.
41.50 x 12,000,000 = 498,000,000 cubic inches of space.
1728 cubic inches in a foot.
288,194.44 cubic feet to house all the ammo needed to kill 6 billion zombies.
insert a bunch of even more math i didn't feel like typing ...

lag - "We need 250 of our family rooms just to house the .22 ammo needed."
cpg - "And that's without missing ... "
lag - "You wanna figure out how much room we're gonna need for the barrels?"

oh, you know ... we only need 120,000,000 more of these boxes