This is the first time that I've read the full ME's report.
Correct me if I'm wrong, but it looks like the bullet only traveled 1.5 inches from where it entered the skull and then through the palate. You realize that this is the area of the brain that was used for frontal lobotomies, right? Longer instruments were used and they went much deeper into the frontal lobe. Those are neither fatal or incapacitating.
This is almost like a mini-lobotomy. Mood-altering, yes. Instantly fatal, far from it.
Edit: Here's a link describing the technique. WARNING, GRAPHIC:
Lobotomy - PBS documentary on Walter Freeman - YouTube
The projectile was only 1/8" in diameter, according to Horn, the ME.
Horn says he was not able to get any evidence from the brain, as it had decomposed faster than other tissue.
Gun first.