Aiming for a bear's head is actually a very bad idea. The skull is very thick, as is the hide covering it. The small brain is well protected. Worse yet, the sharp slope of the skull can cause bullets to ricochette off, just enraging the bear. Unless you can place your shot from underneath and into his brainstem and spinal cord where it enters into his skull (if he was rearing on his hind legs over you), I would recommend against a head shot attempt in the heat of self-defense. Even then, it should be an upper-throat shot.
I would feel more confident trying that with a 12gauge and 00Buck at close range. Literally try to blow his head off. You might instead blow his jaw off and all he could do then would be decapitate or eviscerate you with a single paw swipe, but at least he couldn't eat you afterwards and he would eventually die, too, from starvation.
I'm not by any means trying to give more immortal legend to a bear than is reasonable. They can certainly be killed quickly, but that is not often the case. I killed one stone-cold-dead almost instantly with one arrow. But that was a very lucky shot on a bear that had chosen flight rather than fight at that crucial moment when we were locked eyeball-to-eyeball. That's a really weird feeling, suddenly understanding at that late moment that it is indeed his decision alone and it could go either way.
My arrow sliced through him completely lengthwise and crosswise from behind his rearmost rib taking out his liver, both lungs, and severing the aorta off the top of his heart before exiting his opposite armpit and forever being lost in the heavy brush. He made one whirling, lightning fast lunge and hit the ground dead with a huge 'whooshing' sound like someone had just kicked him hard in the 'nards.
I was trying for just the lungs since the heart is even more protected by heavy bone, muscle and hide, and location, than the brain. I don't care what critter or what size: If you put big holes in both those lungs, it will die; just not necessarily right away, and that's where the problem with large, potentially ferocious critters that are better-armed than you comes in.
Even he covered several feet in that one lunge and I sure wouldn't have wanted to be closer than I was at 25 yards. Arrows (broadheads) have zero knockdown power and you wouldn't even get a second arrow nocked before he covered that small distance, even if he was mortally wounded. That was just a 350 pound black bear. Respectable, but nowhere near huge. A grizzly? Forget it. My arms felt like limp spaghetti and my knees were knocking as it was when I drew back...
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