I've seen 22 solids go thru 2x4s and plywood, and I gotta think that hitting a kneecap or shin bone, or even a foot shot would pretty much make that limb useless.

When I shoot sub-caliber for self defense, I always aim at or below the belt buckle. Most times the fight's over if they can't walk anymore. In fact, the same goes for sd loads on the shotgun.

Even major caliber head shots are a waste of ammo in a self defense situation.

For what it's worth, the 22 lr is a more suitable sd cartridge than the 25 acp. Standard loads are more powerful, the weapon selection is better, and both cartridge and firearm are more economical.

Now there was a time when a company named Grendel made a nice semi auto about the size of a springfield 45 that chambered the 22 mag, with a detachable box magazine that held 30 rounds. It wasn't a particularly high quality firearm, but it was reliable enough, and the muzzle blast on that 3" barrel made it look and sound like a 357 magnum, especially at night. Yep, you could get everyone's attention with that little shooter.

Personally, I think the 45 acp is the minimum effective self defense cartridge. Of course, like someone else said, it ain't much for small game hunting, especially if it's meat for the pot.