Unusual question
Perhaps it is because you are new to guns. It is a small thing, but words carry meanings beyond their dictionary definitions, and in a court they carry legal consequences as well.
Asking what is the most lethal bullet when talking self defense is considered bad form. In a court it is much worse. When we talk about self defense ammo, we use the term "effective".
Effective at stopping the attacker. Not killing them. Stopping them.
If an attacker dies as a result of being stopped, so be it. It is not a concern, as long as they are stopped. Most states laws are written so that you are only justified shooting someone if they must be stopped from harming you/others. You are allowed to use "deadly force" to stop. You are not authorised to "kill".
Lawyers, prosecutors, courts, and cops understand the word "kill" to imply a premeditated act. This can get you in all kinds of legal trouble if you ever have to shoot someone in self defense. Just as you train with your firearm, you should train the way you speak. One does not shoot to kill (that is murder), one shoots to STOP an attacker, that is self defense. One never shoots to wound. Saying you only meant to wound implies (to the law) that in your mind, deadly force was not justified. And if deadly force is not justified, then you are not, legally, allowed to shoot someone.
Sorry for the language lesson, but it is almost as important as your physical skills with a firearm. Train properly and your skills will protect you. Your choice of words, and the impression they create may be the difference between a decision of justified self defense and having to defend yourself again in a court of law. Seriously, think about it.
Now, as to your .22LR question, here goes;
I have chronographed a number of regular "High Velocity" ammo (40gr bullet) from several different 6" barrel .22 pistols, and they all get around 1250fps, allowing for the variation found in individual guns.
Stingers, Vipers, Yellowjackets, or other "hyper velocity" rounds are faster, and use lighter (usually 36gr) bullets. Out of a pocket pistol, you lose velocity, 35-50fps per inch of barrel. There is a lot of individual variation in the amount of loss, due to variables in the gun, and the particular ammo.
So, out of a pocket pistol, you could be down to 1000fps, or even less. NO .22LR has any excess of energy available for self defense use, and out of a pocket pistol, you are on the bottom of the available energy scale. Only precise shot placement is effective, and even then it may not work 100%.
When you are talking small game hunting, there is a significant difference in the effectiveness of the standard and Hyper velocity rounds. Against humans, the difference is not nearly as significant.
If, because of your circumstances, you must rely on a .22 pocket pistol for self defense, I would recommend using whatever ammo proves the most reliable functioning and accuracy in your gun. And relibility is more important than a small difference in group size. Whatever shoots to point of aim and feeds, fires, and ejects all the time (even if it does not produce the smallest groups) if what I would choose.
Hope this helps.
