KCitons
Footballguy
Part of the reason experts suggest a 12 gauge for home defense is to prevent penetrating walls.A 9mm will penetrate multiple layers of drywall with no problem, on par or better than a .223 depending on the respective rounds. Many 12 gauge loads will penetrate multiple layers or drywall as well .
Search "best weapon for home defense" and you'll find multiple comments about shotgun vs AR15 in regards to wall penetration.