It's been my personal experience that Bears, whether Grizzly or Black are extremely fast, when the curiosity wears off and they decide to charge.
I have a standard method, I point the firearm I have in hand at the ground, in front of the route the Bear has to take to get to me. Usually it's straight on.
When I see fur in the sight, I pull the trigger. What I really want to happen is that the Bear is temporarily disabled, so I can finish it with an aimed shot.
That spot is approximately 15 meters away.
When a bear is charging at full run, there isn't time to calmly aim that firearm. All there's going to be time for is one shot, bolt/pump/semi, at that distance.
You're first concern is to stop it. Then, if you've managed to hit it hard enough, place your shot where it will slow it down some more. When their adrendilan is shooting through their veins, they recover very quickly. A Grizzly heartbeat is appx 12 beats per minute.
As for slugs, they work, if your first hit is a good one and you can get another into the chamber on on target very fast. I prefer 000 buck shot.
I want to maim and mangle, so that I have enough time to finish the job properly.
Anyone that's been charged by a Bear knows that it's an extremely stressful moment in their lives.
I've been charged by Grizzlies more time than I can count. They have a great sense of smell, but are very near sighted.
Charging is an aggressive tactic they learn at a young age and it's as much an intimidation action as anything else.
I had one Grizzly stand on its hind legs about 50 meters down the trail from me. I had a camera, instead of a rifle in my hand. I won't make that mistake again.
He was swinging his head back and forth, while making loud coughing noises and slobbering all over himself in the process.
I ducked for a small Pine tree, appx a meter on the side of the trail, when his head was at the end of its swing.
That bloody Grizzly charged when it brought its head back and ran right past me. I was scared to say the least.
The Bear stopped about 10 meters past where I had been standing. Its hair, which had been all fluffed up, which made it appear twice its real size, started to flatten out and he sat down on his haunches, looked to the right and left, then got back onto all four paws and started walking down the trail, in front of him as if nothing had happened.
Why he didn't turn around to look back I have no idea. I wasn't complaining and it took me close to an hour to quit shaking enough to head back to camp.
One of the old timers there, told me a similar thing had happened to him on a previous hunt a few years before.
It's nerve wracking to say the least. I couldn't pull it together enough to go out on a before dark hunt. Even the next morning I was apprehensive.
Grizzlies charging is their biggest mistake and gets them killed when there isn't a reason for it.
They have a habit of charging, especially young/aggressive boars, until they can see what they're actually looking at. As often as not, when they see or smell HUMAN, they turn and run in the opposite direction.