One item that soooo many people shudder in their boots about is having a bullet that you fire go through the BadGuy(BG) and hit some innocent person beyond the BG. It seems to be one of the favorite subjects of many gun writers. In my reading I found the FBI report on the 10mm which became the FBI recommended round for a short while. The 10mm was chosen because of the penetration it attained, and some worried it would be too much.
The report was written by:
SSA Urey W. Patrick,
Firearms Training Unit
FBI Academy, Quantico, VA.
Written about November, 1989.
I will quote a small portion of that report that details their conclusions on over penetration.
Q:Aren't you afraid of over-penetration?
A: The fear of over-penetration is a misconception, which was created back when law enforcement was trying to overcome misinformed public resistance to the use of hollow point ammunition. In the process, we began to believe it ourselves. First, our lawyers are unaware of any successful legal action resulting from the injury of a bystander due to a round over-penetrating the subject. We are aware of numerous instances of Agents/officers being killed because their round did not penetrate enough (Grogan and Dove, for example). Further, if you examine shooting statistics you will see that officers hit the subject somewhere around 20-30% of the time. Thus 70-80% of the shots fired never hit their intended target, and nobody ever worries about them - only the ones that might "over penetrate" the bad guy. Third, as our testing shows, even the most frangible bullets designed specifically for shallow penetration will plug up when striking wood or wallboard and then penetrate like full metal jacketed ammunition. We are aware of successful legal actions where an innocent party has been struck by a shot passing through a wall, but as we have proven, ALL of them will do that.
With any luck, that should let at least a few more people sleep well at night.