Forget about the rifle calibers. Any good strong rifle bullet in a powerfull cartridge is good on big bears when the range is far. The 45/70 in levers and the 338 in bolts should be the least you take in the field. A shot through both lungs in those calibers will drop any bear in 100 yards or less 95% of the time.
A charging bear is a completely different animal in a completely different situation. The range of a bear charge is measured in tens of feet not hundreds of yards. He is generaly either enraged or hungry and needs to be stopped right now. The gun you need has to be one you can carry and have ready to shoot 100% of the time. You need to be able to wield this gun even if the bear has you on your back and is tearing at your head. That eliminates all long guns. It has to be uncomplicated and capable of functioning even when you can't. It has to fire even if you can't cock the trigger. Forget semi-auto handguns. It also has to be able to drop 1000 pounds of angry mussle, tooth, and claw before it can eat you.
I'd say at least a .454 casull in a double action sixgun. Keep the hammer down in an empty chamber but keep the others full. The gun won't fire if dropped or hit hard but one pull of the trigger and it will go boom in a big way.