>>527032
>ANYTHING that will reliably stop a human target will penetrate the walls of your standard american home/apartment.
This is not true at all, and for this reason a handgun is, in a way, perfect for home defense. I hate to recommend 45 auto or 40 s&w for any reason, but there are plenty of loads in these calibers that will expand to double their size, blow a big old hole in a person, but just barely meet the 12" FBI penetration standards. Something like this is the gold standard for anti-personnel purposes where overpenetration is NOT an option.
Look at the classic 110 gr. semi-jacketed hollowpoint in .357 magnum. Piss poor penetration, but wide, reliable expansion (for the time.) This load was specifically developed for the Secret Service, who figured the most likely defensive scenario would be shooting an unarmored guy in a crowd.
I guess what I'm saying is that the 12-18" penetration standard for the FBI was created with barrier penetration in the field in mind, but in reality you need a lot less than that for a typical home defense situation. It's really all about the expansion for man-stopping.
Check out
https://www.luckygunner.com/labs/self-defense-ammo-ballistic-tests/
The most amazing thing on that page is the 230 gr. Winchester Ranger T in 45 auto. 1.00" expansion, with 4/5 test rounds being on the low side of the 12-18" standard through thick clothing. This would be a nearly IDEAL round for home defense, as you can be pretty damn sure that all that energy would be dumped into the target.