There was no time for changing ammo and eye contact has to be maintained on the bear.
Could have been time when the bear 1st turned away, however the sound of the gun might have provoked a quicker charge while changing ammo.
It's all speculation. If inside 10'(3 meters), the bird shot in the forehead would have done the job, especially 2 of them.
We were taught first blast at 12' using bear spray on grizzly.