A shotgun with slugs is good bear medicine, but so is my .45-70.  As for handguns, a Casull ain't bad either.  Ballistically, it's very close to a .45-70. 
In the area I live and up in northern Canada, many outdoors and wilderness workers  carry a Marlin 45-70 lever action for bear protection. This rifle and caliber will bring down any bear....grizzly, black and polar.