Guys, penetration has more to do with ballistics and physics than it does caliber size.

If someone shoots two people that are "stacked" on top of each other, ie. screwing, fighting, bear hugging, then there is a large likelihood that any round will go into both.

The FBI's penetration threshold, going off memory here folks so don't go crazy, is 13 inches for ammo to be considered "effective". They want this amount of penetration because AT WORST CASE SCENARIO the "perp" will be shot CROSS TORSO, i.e. the widest vital part of the human body, and therefore they would like any ammo used by LEO to be able to penetrate that. Again, very small calibers can penetrate 13 inches and some even beyond. That doesn't automatically mean that they are "man stoppers" or will drop anyone in their tracks. It just means that at X velocity with Y grain bullet, it penetrates 13 inches or so. Again, that's just basic physics and ballistics. You can fire a dart deep enough to penetrate 13 inches, but that doesn't mean it's going to stop your attacker any faster than a .380 bullet that only goes 10 inches.

Stopping power is all about FIRST placement and second ballistics. We can go into a gigantic debate on wound ballistics and stopping power of every caliber, but suffice it to say that little .380 bullet hitting mid torso is more likely to stop someone than a flechette hitting in the same spot. Why? Likely because the .380 bullet will create a larger wound cavity and channel than a flechette will therefore the likelihood of incapacitation is going to be greater. Again, I don't want a ton of debate back and forth about this because this is a very far fetched example for illustration purposes only.

Bottom line is that shooting at a tumbling and rolling mass of people fighting is a BAD IDEA to begin with. Second, Critical Defense ammo or not, the likelihood of over penetration is always there, so pay attention to what's behind what you're shooting at. Finally, shot placement is far more critical than ammo choice. A .22 to the chest will kill you faster than a .50 BMG that misses the target all together. Think about it.

There's an old saying, "Rather be judged by 12 than carried by 6". I'd rather take my chances in court after killing an attacker than my wife becoming a widow because I decided to be coy about someone meaning us harm. I would shoot an RPG in an attacker's mouth if I got the chance and it's all I had.....or try to get him with a bent paper clip if that's all I had.

What I find really comical quite often is brand new gun owners.....total newbs....that worry so much about caliber and ammo. Why? Can you even hit what you're aiming at yet? Then it doesn't matter what you put in your hands to defend yourself with, right? People need to realize that owning a weapon for defense is a very real decision that is not to be taken lightly, so you better know what you're doing if you decide to do it. You can buy a freaking Howitzer and mount it on the roof of the house, but if you don't know how to load it, aim it, fire it......it's as worthless as tits on a hog. Might as well throw rocks at somebody cause you'll get better results.