I think shooting and killing a charging T-Rex should be the ultimate dangerous game experience ever ! But If you miss it, I think it's definitely over for you !
According to the size of its brain in comparison to its head, I don't think the brain shot is the best way to stop it. I don't know if it is easy to knock them down or at least it to deflect their trajectory if you miss the brain with a big bullet providing a lot of momentum ?
Maybe we can find more infos in this book ?
Since the animal is standing upright, a spine shot would be probably more effective as the target is a bit bigger and more easy to locate ?
Some PH carries a handgun to their belt as a last ressort but with a T-Rex on the menu, it is probably not the wisest choice !
I would be more confident with a rocket-propelled grenade as a back up gun and that should drop it on the spot with a good chest shot. But with this weapon, the full body mount is very compromised....
I will be curious to know what is the best way to hunt such game, too ? From a blind on a bait, by tracking or with an electronic caller ?
I'm sure with my .458 Lott and a good 500 gr CEB safari solid it will be effective. I will shoot it in the body and I will give him a couple of hours before following the blood spoor. However, I will never ever release my dog behind such beast even if he is very prudent. But once again, I can't imagine the adrenaline pumping while approching a wounded T-Rex bayed by a pack of hounds.