There are a couple of different philosophies regarding how to handle a home intruder. One is shoot to kill, no questions asked. The thought here is that if an uninvited person is in my home at 2 a. Same for an unarmed teenager who was badly influenced by his peers.
No, Your Walls Are Not Bulletproof … But They Can Be
What size bullet can penetrate a wall? | Yahoo Answers
Despite the trend for 9mm protection rounds that provide "adequate" penetration, there remains a contingent of people concerned about "over penetration" and the possibility of an innocent third person being injured or killed by a bullet that has completely passed through its initial target. There are also professional people working in extremely crowded scenarios that prefer ammo almost guaranteed to remain within the average human torso. If the average upper male torso is 9" deep, some opine that penetration beyond that is unnecessary. Most scribes consider 10" to be short on penetration and specify a minimum of 12" penetration.
There are a lot of false ideas floating around about what works as cover — in other words, what sorts of things will protect you from getting shot. This has left us with a false idea of how well common items will protect us from the damage caused by flying bullets. In reality, there is little in a home that will stop a bullet.
For most modern. Now note that I said "most," not "all. And some carbines chambered for. Mag safe SWAT rounds are one of the few rounds that won't go through sheet rock.