Depends on where you are going to hunt Black bear.
On the lower end, I have gotten a 250 lbs bear with 7.62x39 and that was OK but could use more power, ended up using up 3 shots. Couple of them in the 300 lbs range using 270 and did very well, ran maybe 20-30 yards. As others have suggested, black bears are a bit more than deer and not much more. Shot placement is everything, I personally like to wait till a good shot angle to break shoulder bones and organs.
Now if you are hunting the bigger black bear such as the ones in coastal NC, those big boys are 500lbs+ and I would definitely up gauge to 308 or 30-06.