Zombie Apocalypse: Crossbow question?

Hey, this is a shout-out to all of you who have read up on your zombies this fine week. I, myself, consider myself mildly educated (at least) on the walking dead, and came across a question the other day.

Well, it’s more of a string of questions. Starting with… “How strong does a crossbow have to be (in pounds of pressure) to puncture a zombies skull?”

I know there are many variables such as how old the zombie is, which affects the mushiness of the bone, but does anyone know an estimate?

I need to know because I was debating on buying a crossbow pistol instead of a real crossbow, despite the major loss of pressure. They look so cool!

SO… Thanks for any/all help and advice. :D discuss!