The whole idea is shutting down their body, so they can no longer harm you. The technique is to perforate their vital organs, or break their bones with fast moving projectiles. The larger the projectile the better, but if all you have/can use is a .22, then do it. I would not feel to inadequate with a ruger 10/22 loaded with CCI stingers in my home. But, I will still prefer my AR15.
As a note, do not take head shots with .22lr pistols as the skull is often not penetrated due to the slower velocity of a short barrel. Stick with pelvis and torso hits.
