I had magnum slugs in mind. Rifling is useful, for longer range shots.
But at ranges long enough for rifling to matter, you're not killing the bear for self defense; you're hunting.

I wouldn't want to kill such an animal unless it was obviously intent to and undertaking to attack me to do me harm. The accuracy rifling would impart to a 12 ga. slug at such range would only mean millimeters one way or another, on the target. And the target in this case is between or in the bear's eyes.
True.  And if a bear's close enough to HIT it right between the eyes, that .45 ACP will do just fine.  Maybe not so much in a body shot, but no, I don't plan to test that.


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SGT. JIRI TREBISSKY H&D SAS

"When the winds of change blow, some people
build walls and others build windmills."
~ Chinese proverb