OK Guys, I'm gonna do something I rarely do. I'm gonna "pile on" with the responses in the prior posts, and agree with Swampy. :-)
The Remington Corelokt, 180 grain bullet, in .30 caliber, will efficiently kill any black bear that walks this planet, whether launched from a .308 or a .30-06 or a .300 Savage. I have no experience with a .270, so I will stay out of that arena.
At least in the realm of the .30 calibers, I believe that any person who nit-picks or obsesses about using premium custom bullets on a black bear may be more interested in fooling with his gun than in baggin a black bear.
Here in the Shenandoah Valley of Virginia, and in Upper State New York, huge numbers of black bear are killed every year, and the .30-30 (with 170 grain Core-Lokt) and the .35 Remington (with factory loaded Core-Lokts) are also extremely popular.
Regards, Mannyrock