Just dealt with a blonde bear (black bear that looks like it got the peroxide treatment), small probably 175 lbs or so. Relaxed by my decorative pond, then wandered towards the bird feeder. Tried yelling at it, threw a small rock, neither got its attention. So I loaded up a rat shot .22 shell and popped it in the butt. It took off at speed. One of our other neighbors must have seen it because the several Sheriff deputies drove up and down the road.
I live in the mountains and have one gentleman that is allowed to hunt on our property and he hunts turkey with a .10 gauge single shot shotgun.
A couple of years ago he was in his blind and heard a noise and watched a monstrous black bear come ambling through the woods walking straight towards him. He stood up and did the usual things you are supposed to do and the bear kept coming towards him. Finally at about thirty yards he said he was calculating he could get one round off for sure, maybe two. He raised hit shotgun up and decided at twenty yards he would open fire. At twenty yards he took aim and the bear stopped, looked at him and grunted, then turned and ran the other way. He estimated 400-500lbs range for this critter.