I happen to have had the pleasure of carrying an AR, and I do own one. I don't have little springs and parts laying around anywhere, I shouldn't need any parts, I have no Blas against them, not sure why penetration matters as long as it penetrates, pretty sure it is also illegal to keep loaded mags in your safe next to your restricted rifle. Not much good if it is in a safe to begin with, which my non restricted shotgun need not be. A simple 3 digit trigger lock one digit away from being open and I am 20 seconds ahead of you at least, seconds count when it's time. If you can train on a AR sure you can use it CQB, but lets face it most never take it that far, I can tell you a .223 may not stop your perp, but a chest full of 00 they will be on the floor. Plus I can put any kind of shot for most types of game, including deer, and moose. AR is a one trick pony with your average Joe running it, things to fail on an AR platform? Operator
ammo mags extractor proper lubrication those would be the most common causes of failures. then further down the line would be Springs Pins Gas issues, charging handle latch PIN, The damn BCG, bolts break as well, firing pin. Any of this stuff breaks your AR is useless Gear is great, but training is the key. Ar's are cool but they are not survival guns