Randy Garrett seems to know what he's talking about with regard to handgun defense from an attacking bear:
http://www.garrettcartridges.com/031000.asp
His hard cast cartridges are nasty to shoot in .44mag. I've tried similar hardness/meplat cast bullets in .454 Casull and I think they are pretty nasty too. HOWEVER, you'll probably never notice in a real bear attack scenario.

To everyone who actually doubts they'd be able to make a killing shot or instantly incapacating shot on a Griz. with a firearm... in a bear attack (and frankly, that should include all of us!) why not consider Bearspray (or Wolf spray, or Cougar spray, etc.). Look at the data:
http://mountain-prairie.fws.gov/species/mammals/grizzly/bear%20spray.pdf

Forget the "head shot" by the way. What you're after is the "up the nose to the brain" shot. When I told my guide "That's a pretty small target to hit on a charging Griz." he told me: "If you'll just wait a moment, the target will be a lot bigger".