when this game up, I was reading a couple articles about it . I read one about a guy who had a guide with him. he took a shot at the grizzly and it charged them very quickly. he said the professional guide took 15 shots and the grizzly kept coming. it wasn't until he he got a throat shot that took down the grizzly. this bear withstood 15 rounds into him and still charged, uphill full speed.
I read another article that said black and brown bears were killed easily with hand guns.
I haven't done much research, but it seems grizzlies are a much different breed than other bears.