If you "need" to hit a charging bear, it's better to hit than miss. If missing is possible, I'd rather miss in front of rather than over a bear. "Spraying" a bear with debris seems, IME, to be a lot more effective than just making noise at them.

The following vid shows several things which seem to be true about bears from what I've seen:

-they are often easy to "drop"

-a "dumped" bear will often recover very quickly

-they move real well when they are motivated

http://www.youtube.com/watch?v=LZnsL7-UdGc

BTW, 170 grain RN Corelokts (30-30) penetrate better than 2 3/4" standard Foster type 12 gauge slugs.

Sometimes, the air you 'let in'matters less than the air you 'let out'.