Honestly, I'm not sure it matters - as long as it is a quality bullet. Any bullet you'd shoot a hog or deer with should be fine. As cliche as it sounds, shot placement is key. I've killed several bears while hunting and in my former profession. They're not particularly hard to kill, poke a hole in the lungs or put a round through the CNS and they die.
If I was going out to intentionally kill a bear, with a Grendel, I'd shoot the 129 ABLR. I have a good supply loaded and it shoots well in my 12" gun.
If I was going out to intentionally kill a bear, with a Grendel, I'd shoot the 129 ABLR. I have a good supply loaded and it shoots well in my 12" gun.