If a grizzly charges you, you will be faced with a frontal shot with very little time, probably under 2 seconds to shoot. At this point you need to hit the CNS (brain), those nice behind the shoulder shots most likely will not be available. Bullet construction, sectional density and of course power to some extent are most important. To say you feel save with a 44 Mag but not a 270 doesn't really make sense to me unless you shoot a lot better with your 44 Mag.
A study was done recently regarding the effectiveness of hand guns in stopping bear attacks. The results were surprising in that handguns were effective like 95% of the time! Even more surprising is caliber didn't seem to matter!
So ask yourself why?
As most things the devil is in the details. The majority of the handgun defense cases the bears weren't killed , simply convinced to find trouble elsewhere I would guess.
Another detail is the hand gun can be deployed at very close range, odds are you are going to get bit.
A rifle is a one and done deal usually. If the bear gets ahold of you the rifle likely cannot be deployed at that point, while the handgun can, keep pumping rounds into him!
