1. Can you supply evidence that any grizzly has survived multiple shots from a .357 cal Magnum? I find that hard to believe, since the skull of a bear is only about twice as thick as that of a human and the brain behind it is equally fragile.
2. Grizzlies are not 3 times the size of gorillas; they are less than twice the size, and half their bodyweight is fat compared to the gorilla which has very little bodyfat. An average mountain gorilla at 450 lbs actually has the power advantage over the average 800 lbs bear.
3. Running fast doesen't mean shit unless if it is to run away from the fight, in which case the gorilla wins by default. Can a sprinter beat a pro MMA fighter in a fight? No, even though he can run faster.
4. A bear's claws would not cause any lethal damage to the gorilla unless it hit the carotide artery on the neck or poked the gorillas eyes out. Both are unlikely to happen in a fight. The gorillas canines and biting pressure, it's freakish arm strength and dexterous hands are more formidable weapons than the bear's paw swipes.
SUCKMYMUSCLE
First of all a Kodiak--not a grizzly or polar bear should be used as the exemplar of bear mightiness.
Kodiaks, despite being slightly smaller than polar bear in terms of weight, have much thicker skulls, and are covered with dense fur and fat.
It is thought that, as polar bear habitat shrinks, they will lose out to kodiaks as they are forced to compete with them in the same niche environment.
You said that when stripped of their fat, bears of comparable in lean muscle mass to gorillas, however what you failed to mention is
this layer of fat actually assist fighting, not hinder it. Similarly, the Chinese Shar-pei was bred to have excessive layers of fat folds, to protect it from grievous wounds by other dogs.
Kodiaks weigh 1000-1200 pounds, and a silverback standing upright would barely stand taller than a Kodiak's SHOULDER. Standing upright, the massive Kodiak is around 10' tall--
dwarfing all silverback gorillas.
Silverbacks have a powerful bite, but their bite is nullified because a silverback has a short muzzle and dull teeth, that wouldn't be capable of penetrating this kind of dense fat layer. That is assuming a gorilla would get past the Kodiak's claws first...
Kodiak bears have claws approaching 5" long!!! A gorilla's lean muscle mass would work against it, as it stuggles to grapple with the neckless bear. The kodiak would tear through it's flesh, raking it with it's claws until it dies.
