I don't really have a dog in this fight, but one thing I've heard from "gun enthusiast" family members is that this is fine if you're imagining an "ideal scenario" of being barricaded in your room waiting for the cops to show up, but it's worth considering what can go wrong - compared to a shotgun, an AR is much easier to operate with one arm (if you just woke up and one is asleep, or you were involved in a struggle that disabled one, or whatever); much less recoil (could be an issue if smaller family members need to use it); faster rate of fire and more rounds available before reloading (in case you miss or there are multiple attackers).

- Houses that were penetrated by stray .223 rounds from football fields (aka multiple hundreds of meters) away probably weren't rounds shot through drywall. Maybe from outdoors, or through a window, who knows.

- .223 rounds that encounter no obstacles in flight have a flat trajectory of about 200 meters (2 football fields). .223 rounds that penetrate any substance of sufficient density have their flight path altered.

- In my limited experience with buckshot (none with residential materials), it's probably going to have a relatively flat trajectory, even through drywall. Something to especially consider if you have other people in your home.

22LR doesn't tumble.

>Here's pricy specialty frangible rounds designed not to go through walls... still going through walls in a test:

Frangible rounds are usually used so it doesn't ricochet and hurt someone. It just becomes dust when it hits something hard that would normally bounce a bullet.

Contrary to popular legend, it does not tumble in flight.