Professional Hunters in Africa know to get down on one knee when faced with a Lion charge so as to minimize as much of the elevation aspect of shooting an animal moving at high speed. If the animal is coming at you and you are standing, there is SOME lead that needs to be applied, but I can't tell you how much. Depends on the any number of things, the height of the animal, your height, speed of the animal, size of the target and lastly the ballistics of the weapon you're firing.
Really, the best way to figure this out, is to assemble a moving target to replicate as much of the situation as possible. I've seen this done by putting a car on jack stands, then rigging a pully system to use the cars wheels to power the pully that pulled the simulated Lion. Saw this years ago at a shooting contest for double guns. It was rather clever and worked remarkably well.
If you really think you could be facing such a situation, then it's worth your effort to construct such a monstrosity.
But you need to be very realistic; are you REALLY capable of putting ONE shot precisely where it needs to be under such circumstances? In a charge situation, I would say that 99.9% of all shooters are probably better armed with bear spray than a handgun. Certainly there are some who can get it done with a handgun or a rifle, but there are far more who can�t. Just be-bop over to Youtube and look at all the Professional Hunters that botch the shot; AND THAT�S THEIR FRIGGIN JOB!!
