At first I thought: "Man, again somebody talking about guns/ammo who does not have a clue.." But after reading the whole post, I must admit, that you have knowledge about rounds.

Although the Deringer wasn´t designed to shoot someone in the head. It was more a selfdefense gun where women were able to shoot from short distances.
The problem with .22 is the lead which almost exlodes while creating the wound. MAking it more difficult to retreat the lead from the wound.

I used to shoot hollow point 9mm with 115grain from my 1911.