You will pardon my skepticism
You wrote: "a hunter from Denver last year hit a grizzly with several rounds from a .475 H&H (he was a good shot, too) and still it kept coming."
I doubt if he was a good shot. A single well-placed round from such a high powered weapon will shatter a bear's skull and turn his brain into mush. A round through the bear's heart will stop the heart cold. A round through the upper spine will paralyze the animal. Etc, etc. A .475 H&H is an extremely potent big game rifle with a muzzle energy in the range of 6,000 to 7,500 foot-pounds depending on the particular load and a kick like an angry mule. A well placed shot from a .475 H&H will kill anything that walks on dry land.