So if I fired a gun close to the head just to scare someone, and it blew their brains out, what would I be guilty of?
Manslaughter. You might well end up in proson for as long as you would for murder, but lacking the mens rea to kill someone, mean that it cannot be murder.
No, as there's no intention of killing someone--with a bit of bad luck, that might be the outcome, but it's still a different thing.