The conclusion I get from the accounts is the best handgun bear defence is a handgun, in the hand and the ability to shoot it. Discounting the .22 RF examples which were often black bears and climbing a tree. Even a 9mm s/a pistol will work to stop an attack. Especially with fmj ammo.

If purposefully carrying to kill brown bears, yep a .44 magnum might be the best.

But whatever it is it needs to be in one's hand or quickly accessible when needed. The biggest heaviest cannon is useless if in the backpack.

Sadly no .58 Howrah examples.

PS again our own member Phil Shoemaker is mentioned. Do a search for the one or two threads where it is mentioned.