The tiny 3 grain bullet has a muzzle velocity of about 650 feet per second. That means that the gun has about 1/2 the power that an air pistol produces. The projectile is so small that it would certainly penetrate if you shot someone's bare skin, but it also means that I really can't conceive of it doing anything but pissing an attacker off.
Unless you managed to shoot his eye out, of course.
Found in comments at James' place