As Jerry noted, death would be instantaneous. You can get a concussion from an impact of less than 10 mph (16 km/h). Your brain would be destroyed by the impact if you were at terminal. There would, of course, be broken bones and severely damaged internal organs. But it would be the neurological damage that would kill you instantly.
I've had this discussion at the DZ (not surprisingly). General consensus is that you wouldn't even feel pain. Just one hell of a thud.
Lots of people have survived bullets to the head. Damage is dependent on the size of the bullet and (mostly) on the energy at impact. Death is dependent on level of damage and it's location.
For example, US congress member Gabby Giffords was shot in the head and survived. It was a pistol, which has pretty low energy. She had a very long, difficult and not complete recovery, but she survived.
OTOH, President Kennedy took a rifle bullet to the head. Look up the autopsy X-Ray images and you will see how much of his skull was destroyed.
It doesn't sound to me like you are planning to harm yourself. More like youthful morbid curiosity.