Also consider this before choosing a .22 for self defense: should it ever come to be, you might very well find your incident under review of a grand jury, filled with lots of people who don't know jack about guns. As such the only thing they're going to hear is that you emptied the entire magazine of 10 rounds into this poor wayward soul. Or 7 rounds or 8 rounds, or whatever.

Never mind the fact that all 10 rounds of .22 combined will have less energy than one shotgun blast of 00 buck.

But with the latter, the uninformed jurist will see you as a responsible citizen who was forced into protecting yourself, and exercised restraint by discharging your firearm one time. With the former, you'll be a bloodthirsty vigilante who fired as many bullets as you could until the Hollywood click-click-click thing happened.