Hand gun should be at least a 357 Magnum or more powerful.
.454 Casul works pretty well agains large carnivores (I’ve heard).
While I like your choice of caliber, I am going to shoot the animal with whatever I have at hand.
I am one of the few people on this forum who has actually shot a mountain lion. Of course that was with a .308 rifle, but it was a "good" shoot. It was eyeing me and my dogs, deciding which would be the easiest dinner.