My earlier post was rushed to provide the answer to his question regarding load data. I had to run out for awhile but agree with wanting to use a heavier pill and with either Grizz or Polar bears, 400gr would be my minimum. If not a Swift A-Frame, then a good HCL bootlit would do the trick. It's all about penetration with big bears. I've been bluff charged by a Grizz and trust me, I was carrying my 35 Whelen w/250gr pill at the time but felt there is no such thing as too much gun. And a polar bear is larger than a Grizz.
Then again, we have a member who is an Alaskan guide and his rifle choice is a 444Marlin loaded with Hornady's 265gr superformance. He shot a bruin of a Grizz at close range and it was dead before it hit the ground.