Look guys, we are not talking about a hunting season here where you can take your time to line up a perfect shot, or the bear exposing it's side, frontal CNS and said " go ahead human, take your best shot".
We are talking a defensive situation here. If a bear is not threatening you, you will have no business to shoot it. What is bear posture to threaten you? If it is standing up on it's hind legs then you have no business shooting it. If it is walking toward you, or charging toward you, you'll have only it's frontal target to shoot at, which is it's head, front legs & shoulders. If you feel confidence in that situation using a .22 or a .45, you have bigger balls than I do. In any case, constipation will no longer be your problem.