I have seen pics of PA black bears in the 500 pound plus range, that is lower 48 grizzly size. Hardcast will provide one shot kills if properly placed without question, but it seems the only way hardcast will stop a bear attack is with a CNS shot. In a defense situation that will mean a bear charging you so your only presentation with be a big bouncing head coming at you. If you can hit a target a little bigger that a softball (black bear's brain) while it is covered-up by something a little larger than a basket ball (black bear's head) and do it while said targets are BOUNCING toward you at 30 MPH, then a 357 or larger hardcast will save your bacon. Once you have been hit and the bear is on you, be careful not to shoot your foot or arm or knee that is in the bears mouth just a couple inches from your softball size target which is now shaking you vigorously from side to side. That is the almost certain scenario if you are going to try to defend yourself from a charging bear with a 357.
ArchAngel, there are a few things that you can do to increase your odds of survival regardless of which round you use.
1. Drop to a knee to take your shot if possible. This will save you from having to "lead" your shot as the animal charges you at a high rate of speed. If your gun is nearly level with your target, you can simply aim for the brain, not in front of his nose.
2. Put a tree, a large rock or some other obstacle between you and the bear if time and circumstance allows. The bear will either have to slow down before reaching you to avoid the obstacle, which will allow you a better chance at an aimed accurate shot, or the bear will hit the obstacle and slow down, also providng you a better chance at an aimed accurate shot.
3. You will have 6 shots, try to make as many count as possible before the bear is on you, but don't count on the bear allowing you more than 2 shots to turn, slow or stop it. If it turns, slows or stops, then you quickly try to brain him as many times as possible
4. With a 357, I would seriously consider a 158gr JHP loaded to the highest velocities I could get from them or a 180 JHP if you could find one that would reliably expand. I would load these JHP's for the first 2 rounds in the cylinder then load 4 hardcast behind that for braining or breaking shoulders in case the JHP trauma turned, slowed or stopped the bear the way the 44 mag JHP nearly always does.
Of course there is always the 22LR option for bear defense. Just shoot the next nearest person to yourself in the knee with the 22 and run. If they start to gain on you, even with the 22 hole in one knee (which is a possibilty if being chased by a bear), shoot them in the other knee. Remeber, you don't have to outrun the bear, all you have to do is outrun another person.
Note to self: Never hike or hunt with ANYONE that carries a 22 for bear defense.
Roll Tide