Won't hitting the center of the brain with a bullet with sufficient mass work aswell too?
A slug (or any other large projectile faster then sound) won't just slip through brain tissue. It'd violently force itself through, the cavity expansion would be more then enough to destroy the whole brain ==
death.
For the love of god, not under the chin. The movies lie. People survive it and look... well, not human
Yeah. You
could make it work, but I'd make sure at least the expanding gasses would help liquefy the brain. If you need or want this unoptimal tech, tilt the shotgun a bit towards yourself, and push the barrels end as close to your neck as practical for a good shot. It's risky still, I'd put it in my mouth.
Also, another thing to remember is that even on a success your face might de-laminate, like Ronnie Mcnutt.