I wish people would figure out that feeding the bears isn't being nice to them - they end up dead. Unfortunately, common sense isn't common.
That wouldn't be my 1st choice for Blackies, but it would be more than sufficient. Folks have been hunting them with 30-06 (and lesser) for ages quite successfully. They're not the mythical beast some people make them out to be, but they're a big animal with teeth and claws. I'd go with reliable stuff, especially if he's not afraid of humans. The last thing I'd want is to hear a very loud "click" as any bear was moving my way. A couple recommendations:
- Google up good kill shot info. The head shot can work, but you have to realize that the CNS is relatively small compared to the skull. The lungs/heart shot is probably the best bet, but you need to realize that they're slightly differently-located than in a deer. [Edit: with the caliber you're using, the shoulders and forearms can screw up a clean-looking shot on them, so take a look at their anatomy - the body shape of a bear obscures the location of those big bones, especially if they're shaggy]
- Make sure you understand the laws in your area. I think best bet is to get yourself a tag and wait till bear season, if you can. Otherwise, you'll be explaining things to DNR, and depending on your local folks, they can be reasonable or not so much. If you're going to shoot for defense, make sure the situation is set up right to defend such an argument.
- I wouldn't plan on SSS. Even with a good shot, there's a better than average chance he makes it off your property, and that means a better than average chance you'll not be able to execute the 3rd "S" effectively.