The reason I ask in all seriousness is that so often folks here are asking what is the best kind of shotgun for self defence, frequently also asking the kind of loads required to stop a bear.
I too have shot lots of of bears, but have never come close to feeling threatened by one.
Really, I wonder how serious a threat bears are.
One of my neighbours got a PAL and then bought a 410.
He had once had his tent knocked down on him by a bear in a campsite.
I asked him what he wanted to make the next bear mad for.
But along with many of us here, I don't usually go into bear country without some kind of backup.