.40 cal pistol round will penetrate through sheetrock, etc far more than 5.56. The smaller 5.56 bullet typically disintegrates. with .308 overpenetration is a real problem in urban areas. I never thought of 5.56 as very loud shooting outdoors, but apparently firing one inside will wreck your hearing. A suppressor is a great idea. I am surprised the AR platforms chambered in pistol rounds are not more popular. I would think an AR chambered in .45 ACP would be the ultimate home defense weapon. At the end of the day, the best home defense weapon is the one you can access. That means having weapons, probably pistols, located around your house. Tough to do if you hae children around.
1. Haven't seen AR platform in .45 ACP per se, but Hi-Point has .45 cal semi-auto carbine... similar. Henry has lever carbines up to .44 Magnum. 2. "Guns in the house" with kids around... big concern.
This is what I had in mind. http://www.thetruthaboutguns.com/2012/08/tyler-kee/gun-review-jr-carbine/ It's not strictly an AR platform, as it is blowback operated but it uses AR furniture.
Complaints are comparatively rare. Most of the time they just arch their back roll their eyes up and...wait...what are we talking about?
Hi-Point has carbines in 9mm, .40 cal, and .45 cal... for $369 @ Cabelas... made in America, lifetime warranty. I know, gun snobs poo-poo Hi-Point... but those who own them give them excellent reviews... including me. (I bought one "for the heck of it"... liked it so much, bought 2 more.)
Don't know if I'm overstocked or not. Won't know until the time comes.. but I won't be pleading with the perp, "hold on a minute while I go to the basement to retrieve my gun from the locked safe". The carbine is small, easy to aim/hit target at home defense range... plus picks up 200-300 fps over handgun velocities due to longer barrel.