If you are looking for a magic projectile that will penetrate flesh and bone to hit vitals but is stopped by a piece of sheetrock, well, that doesn't exist.

How did you determine what would have been "deadly at 21 feet on targets behind the wall"? You think your testing is more scientific than that of the FBI?

i think you are completely missing the point. I am saying that a .223 or 5.56 will penetrate drywall the same as most any round inside a house. Again, i could give a damn what the fbi says about it. I don't subscribe to that stuff. A simple .223 round we tested went thru 2 pieces of drywall a stud and into 2 water jugs. So if you think the Fbi saying that it penetrates less, good for them. It penetrates enough to someone on the other side of that wall. There is no round that isn't going to be dangerous to someone on the other side from any firearm except maybe some high end frangible bullet. But to say an AR is the best home defense isn't necessarily true or trying to defend that it is.. Its a false sense of security. Know what is on the other side because any round will most likely go thru. There isn't a way to say it will 100% penetrate less than a 9mm.. simple not fact. If it penetrates drywall, stud and water filled jugs, I think it would kill someone on the other side or severely injure them. So yah, i stand by my statement that an AR may NOT be the best indoor defense weapon. It may be right for some, but certainly not everyone. Its why i suggested checking out a 20 gauge with #4 shot as a better choice for some.

but to say its good or better cuz it penetrates less, well how less, not less enough to not hurt someone. furthermore, we have tested many rounds in this fashion. I am not new to the firearms world, only new to AR's.. again, our testing has been real world much like you see on ammoquest etc... we just don't youtube it.

Nobody said it will not penetrate a wall... But some rounds will loose energy faster.

Let me guess, your "testing" used XM193 and XM855... both full metal jacket rounds. Did you use any of the rounds that are polymer tipped and designed to fragment? Those rounds start to fragment, tumble, and lose energy when they hit a wall. It very well could be the difference between death or injury for a person on the other side of the wall.

You asked for a round, and I told you to try the Hornady 55 gr TAP Urban. Set up your test... test that round along side 9mm, and #4 buck... Let us know your findings.