I've shot one with a 6mm Remington and 1 with a 270. I've seen em shot with everything from a 22 hornet all the way up to a 45-70. They're not overly hard to kill
My only bear was with my bow; Opening day of blacktail season. I recently inherited my grandfather's Model 81 in 35 Rem., so I intend to take that out, but between the cartridge and open sights, it'll be a short range proposition. I believe he did all his black bear hunting in PA.