Every bear attack I have read or heard about in the Appalachians has been made on women or children. I think the greatest defense against a black bear is being a full grown man that does not show fear. A black bear is not going to mess with you. A griz is another matter. If it comes to it: fight a black bear, play dead for a griz. If a black bear attacks, it is trying to eat you. If a griz attacks you, it is most likely a territorial attack or it is defending a kill or its cubs.
As far as guns go, my woods gun is .44 magnum, but I never really intended it for bears. I am much more nervous about people out on the end of the road than I am about bears, and I think a hand cannon hanging from my hip deters potential criminals. Just about any caliber is going to scare the bejesus out of bear, but you'll want something that can crack its skull, like a .44, to do real damage in a timely manner.
I know a number of women and younger kids read this board. To you I would say, be cautious and respectful of the animals and the time of year. I think most predatory black bear attacks occur in the Spring. Going hiking or fishing with your father, or husband, or friend if you are worried.
To the adult males, I don't think you have anything to worry about. Like I said, I am much more concerend about running into somebody who isn't pleased with the fact that I have stumbled upon whatever they are doing, than I am about crossing the path of a bear. I have had a lot of encounters with bears over the years, blacks and grizzlies, from hundreds of yards off, to within an arm's reach, and every bear I have ever seen didn't like being near me at all, and left at the first opportunity. Just make sure you give the bear that opportunity.
Please take that for whatever it may be worth. I am certainly no expert.
Life is hard. But it's a lot harder if you're stupid.