[jeffgrant]

By no means do I profess to be any kind of ballistics/penetration expert, but I have taken a few bear with both rifle (same .30-06 A-Bolt I've had since I was 16), as well as shotgun with slug.

Much like Jeff said, when purposely hunting bear, it's with the rifle, every time. Nothing beats distance and precision to me. The only bears I've taken with the shotgun have been while stalking deer in relatively thick brush where a rifle isn't as useful. (You'd be lucky to get a shot longer than 80 yards).

In either case, I've never found penetration to be an issue, and personally feel comfortable with either choice.