A normal 2 hour firewall will certainly be pierced if you are shooting steel 4's, 2's and/or 00buck and shooting at it from close up with nothing between you and the wall. But I thought we were talking about home defense.

In a home defense situation you are unlikely to be 5 feet away from the wall and hit nothing but wall. If you have a loaded gun in your hands and are hoping to use it on an intruder I'd hope you weren't only 5-6 feet away from the perp, cuz that would mean you're TOO CLOSE.

I believe that using the normal home defense loads, the few buckshot that might pass though into an adjacent apartment would not have a whole lot of oomph left. In the home regular 4's or 5's will do some real nasty damage in the normal 21' or closer combat distance.

I still contend the shotgun is a better option than a pistol for trying to keep the shots within your own domicile.