RE: .270 for black bear?
I have used my 270-winchester to kill 6-black bears in the past. IMHO any premium bullet that weights 130-grains or more will work just fine. I am not even sure you need a premium bullet? I use premium bullets for everything I hunt so I always recommend them. IMHO Black bears are pretty easy to kill & die pretty easy. The only reason I give them any respect is because they can bite back.
Good luck,
WK