First, almost all bullets go through walls except apparently bird shot (well, less than 2 walls) if there's nothing between the gun and the wall.
I have heard that there is a round for home defense that will not penetrate a home wall but will penetrate a person. True? This would be of a.
Since most inner walls in homes in western societies are made of 9mm ( especially ball or target ammunition) can penetrate many layers of drywall. that theory is not practice and you don't need an intimate knowledge of.
All of your defensive ammo will go through a few walls. No matter If you don't miss, there will be very little need for any other precautions.
We don't even have drywall walls. . A small fast bullet penetrates less than a big , long, heavy bullet from the same brass over the same.