colorado
Good question. I suggest you get ALL of Mark Sulivan's tapes and watch them in the order they were filmed.
You can see how he perfected the technique of stopping a charge, over time. He was good/lucky [take your pick] enough to survive enough charges to illustrate the best plan of action. His technique saved my life.
The "plan" is, when charged you hold your fire until the animal is close enough for you to make a brain hit. No other hit but a brain or possibly upper spine will stop the animal. With a double you have 2 shots. One real close, and if that does not work one VERY close. The advantage of a double is the second VERY close shot, no other rifle gives you that option.

Watch Marks videos, study and perfect his technique.
As I say it saved my life.

I was armed with a bolt action 458 Win Mag [I wished I had my 450 No2 double rifle I can tell you for sure] when a 350 lb Gorilla charged me from 12 yards. I fired at 6 yards, hitting him in the Head and knocking him down.
I must admit, seeing Marks videos, and studying his technique gave me the confidence to hold my fire until I was sure that I could hit with one shot [I had a bolt rifle, remember]. At any distance inside 25 yards one shot with a bolt rifle was all I was going to get.

A couple of months later shooting elephants at 6 yards and 12 yards with a double....
Well I felt I was in complete control, after all I had DOUBLE RIFLE.
When it is dangerous, and up close NOTHING will guarentee your safety more than a Double Rifle.
A bolt rifle or even a single shot, well handled, will work, but a double gives you a BUNCH of insurance.

As to a fast reload, I carry extra ammo in a buttstock carrier by www.murrayleather.com