AR vs. Shotgun for Home Defense

James Rummel takes me to task for my first and second posts on whether an AR makes a good home defense firearm.

As he puts it:

In the second post, Dave devotes the very first paragraph to the issue of verpentration. After that it is rather pointedly ignored. Strange, as I think
that it is the one issue that should be discussed the most.

What I said was:

Let me start by saying that I'm not making a recommendation one way or the other. If you can intelligently explain your choice of defensive tools, then drive on with your bad self. If I decide to equip the hearth and home with an AR, I've got the fact that Uncle Sam spent a bunch of time and money teaching me how to use it, I've fought overseas with one, and there's simply no firearm that I perform better with. Apartments may not be ideal keeping AR rounds out of your neighbor's place, but according to the Box O' Truth, pistol rounds go through sheetrock pretty well too. So maybe the overpenetration concern is universal if sheetrock is all that separates you from next door. I wonder what separates townhouses from each other. Anyone
in construction have a line on this?

I'm not sure where James gets a lack of concern on my part on overpenetration liability in urban settings. I said that if you live in an apartment any round could punch through the walls. I wondered what the barriers are between townhouses, the norm in Northern Virginia. I don't have my place AR-equipped for the reasons he lays out - because I don't know what ballistically separates me from my neighbors. That's concern for overpenetration, and I asked about what separates me from shooting a neighbor. I'm not blowing the issue off.

'Cause houses come in different forms. The average NoVa townhouse was built in the late 1970's or so. If it were a slap-dash early 2000's structure there's no way I'd shoot an AR inside the house, but I don't know how much sturdier the older places are. New construction in parts of Florida is hurricane-resistant, so there's a cinderblock skeleton underneath that retro-Miami Vice adobe exterior. So go crazy down there. Here? My place? No idea.

Checking at The Box O' Truth reveals a few things. In Installment #1, we find out that pistol rounds and .223 penetrate pretty well. Here we discover that shotgun rounds penetrate to a varying degree - small shot not so much (but it doesn't do a good job of stopping a pissed off assailant) - slugs too much. 00 Buck may fit a sweet spot, who knows? In Installment #3, we find that 00 Buck penetrates 8 sheetrock boards, which is 4 walls.

As the folks at Box O' Truth put it:

But doesn't 00 Buck penetrate too much in interior walls to be a "safe" load in a home?
Yes, it does penetrate a lot. But any load that is going to be effective will need to penetrate walls to have enough power to penetrate bad guys. If our only concern was to be sure we didn't penetrate walls, we would use BB guns. However, BB guns will not stop bad guys.

And, as they said at the end of #2:

I have brick exterior on my home. I do not have to worry about any round exiting my home. The brick stopped all rounds tested.

So, we must use loads that will STOP bad guys, and this means that they will also penetrate walls. Be sure you hit the bad guy and do not shoot into walls where innocents are on the other side, because anything short of brick is really just concealment, not cover.

The guys in the comments at Snowflakes in Hell make the case for a short-barrelled and suppressed AR. Which, if you want to shoot a rifle indoors and reduce the overpenetration risk is a good way to go. So is frangible ammunition, as these guys point out. There's a spread of opinion at Uncle's place.

Bottom line:
1. What are the your exterior/dividing walls made of?
2. What bullet weight/type are you using, and through what length of barrel?
3. Will #2 punch through #1?

Calibrate your home defense rounds accordingly.