I've dropped a brown bear in Alaska with using a 44 magnum with a 2.5" barrel. One shot of buffalo bore 300grain. I then had to hike 14 miles back to the ranger station to report it. That was during the day, and I did see him coming. I hit the first time. I can't say that it would be the same if I needed to do it again, especially in low light. I did however spend a few quality years learning to shoot at night.
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