RE: 243 for bear
In the hands of a marksman who will wait for a dead perfect shot with the right bullet for penetration the answer is maybe. Yes the caliber is capable of doing it. The natives in alaska do it with a .223 on all sorts of game.
What bigcountry said about muscle and bone is a bear is the key. Every rifle has a use and the 243 would be not consider in use for bear by a national wide concensus.