In August, Guide Phil Shoemaker was taking two clients to a small stream which had numerous large male brown bears in the area. He decided to take his Smith & Wesson 3953 DAO 9mm rather than a larger caliber pistol because the large males are usually less of an issue. As they approached the stream they heard the large growl of a bear, the bear then charged the threesome and Phil let loose with almost the whole magazine. The bear came out on the short end and so did most people who argue that a 9mm is under powered.
To get a sense of what real bear attacks are like check out this book. Bear Attacks of the Century