ANY projectile fired by ANY firearm has the potential "to over-penetrate" and strike something beyond the intended target. The odds of that happening are very, very small. Both the Police Training Institute @ the University of Illinois and the FBI Firearms Training Unit tell us that out of 4 rounds fired by agents and police officers in combat only 1 round will strike anything at all. The other 3 rounds go out into the world, lose their movement and fall harmlessly to the ground. The fourth round generally strikes something like a tree, side of a building, a car and so on. Only very rarely does a round that strikes its target go through the target to strike something else. Is over-penetration a factor? Yes, it is but not to the degree some people worry about it. Now is light weight shot from a 12 gauge deadly? Yes, it is. I know of one police officer who investigated about 2 dozen suicides and murders where people used shotguns for their killings. A good number of those people used birdshot to kill themselves or other people. Probably about 50% used birdshot. So, a 12 gauge loaded with birdshot is, at close range, as deadly as a 12 gauge loaded with other ammunition types. Like the officer is known to say, "Once that shotgun goes off, there is no appeal in the matter. The results are generally fatal and final." Out of the 24 or so cases the officer investigated, only 2 people survived. One survivor was a girl who still walks with a limp from her shotgun injury. The other was a male who ended up with an artificial foot, from the ankle down, from his shotgun injury. If you feel comfortable using light buckshot out of a 12 gauge for HD or personal protection that is your choice. My personal favorite is 00 buck for me at close range in a one-on-one situation or else use of a slug round. I like the saying of, "Go big or go home." That seems to fit well in most shooting incidents.