In yellowstone, my father was attacked by a grizzly that he spooked. It's really an open question as to what really happened. He was crossing the river, and spooked the bear on the sand bar that he was going to. The bear charged, and he ran for the water. when he reached the water, he went down, and the bear wrestled with him underwater before going back to cover. His waders and clothes were damaged.
While waiting for backup, a ranger armed with a handgun checked on the bear's location. it crossed the water and charged him as well, and he shot and killed it with what he had, the .357.
There is no absolute certainty as to what that bear was thinking. I've wondered for decades now if it was just bluffing, or out for blood. It doesn't matter, because they would have killed it anyway, after being involved in an attack.
The fact is, they neither one of them did the right thing. Dad snuck up on the trout and surprised the bear. The ranger snuck up on the bear, like he was trying to take a picture of a deer. the bear was trapped, angry, and spooked.
In bush, or tighter cover, there's no way either of them would have survived that attack unhurt, there would have been no escape, nor room to fire those 6 disabling rounds.
Regarding a batch of bird shot, I can't imagine that working. I've patterned bird shot, and there is likely to be good chance of missing the eyes. I've used skeet loads on dragon flies, just for fun, and if I can't pop a 4" dragon fly at 30 feet I'm sure as hell not going to hit the eyes of a charging bear. Being as bears have been known to tear open bee hives, I doubt that a load of #7s will chase them back. Failing to blind it, I'm really not sure what good it will do to fire bird shot at something that is big enough to stomp the crap out of other grizzlies for breeding rights. Even right on skin contact will not give the sort of damaging penetration that you need to stop it's heart before it swallows your head.
Not that I really care too much what a person uses in pursuit of his own safety, that is his choice, but this is the one thing suggested so far that seems to have absolutely no merit at all, and I'd hate to think that someone walks away from here believing that a montana pheasant hunter is safe from grizzly because of his shotgun full of #4 or 6.