Occasionally (not as often anymore), some folks will question whether an AR 15 (chambered in the standard .223 / 5.56 mm) is powerful enough.
Powerful enough for what? I ask.
Clean, one shot kills on animals larger than deer - probably not. There are better choices.
Sniping from 800 meters away - probably not. Again, there are better choices.
But I bet it would do in a pinch in either situation.
Here is a story about a polar bear being put down with an AR15.
Heck, if it can take down a polar bear, I'd say it's good enough for anything in North America.