One of the most common searches at Extranos Alley is “how much energy for self defense?”
It is hard to say “you need exactly 324 foot pounds of muzzle energy because…” to such a question.
More people are killed with the ubiquitous .22 than any other caliber firearms, simply because they are inexpensive and common. The caliber is not well adapted to self defense, because it rarely kills instantly and often gives the person shot three to five minutes to do whatever he intends to do, but the .22 will kill. In fact, enough .22’s delivered in a short period of time can, and has, killed grizzly bears.
On the other hand, it is not uncommon to run afoul of someone sky high on a devils mixture of drugs and alcohol, when even the 500 foot pounds from a magnum caliber handgun is barely enough.
So we come back to a “circumstances alter cases” situation, where .22 in the hands of a careful shot may drop an assailant in his tracks, while a .45 bullet that left the muzzle with 500 foo pounds of energy may take a while to stop a lung shot perp.
Personally, being neither recoil or report shy, I prefer a .40 or larger caliber with 400 or more foot pounds of muzzle energy. But that’s my personal preference.
My advice is the largest caliber that you are comfortable with, in a gun that feels comfortable to you.
If you are buying a gun and a .44 magnum beats you up drop back to a .45, a .40, a .357, or even to a 9mm. They will all get the job done – but the less powerful the gun the more important the operators proficiency becomes.
If you have a .22, use it until you can trade up for something more powerful.
It’s your money, your life, and your choice. So you should make the decision.
Good health, Sir or Madame, as the case may be.