The amount of bad phyiscs in this is astounding, so I'll just leave a single sentence here for you:
Small rounds traveling faster = more penetrating power than bigger rounds moving slower.
You are utterly wrong and spreading misinformation. I teach handgun self defense at my shooting range, I know what I'm talking about.
This is not an opinion. It is a fact, and a well documented one. 5.56x45 has terrible penetration compared to most handgun calibers. The reason is as I stated, it is a much lighter bullet traveling much faster, and will deviate and fragment violently on impact with any hard surface. This is also one of the major terminal ballistic differences between 5.56x45 and 7.62x39, the latter having significantly superior penetration because it is a slower and heavier bullet.
5.56x45 M855 is designed to fragment, that is its wounding characteristic, and its threshold is around 2,700 ft/s for this effect to take place. It is not designed for penetration, and in fact, it is meant to fragment to prevent overpenetration.
Here are a few links that you would have seen had you taken the time to google it.
https://olyarms.com/index.php?optio...tion-testing&catid=13:technical-info&Itemid=3
http://www.defensivecarry.com/forum...25105-5-56-actually-may-safer-indoor-use.html
9mm vs 5.56x45 sheetrock penetration into ballistic gel, with the 9mm penetrating 9" into the gel and the 5.56 only 6" after traveling through five simulated walls, clearly showing 5.56x45 having inferior urban barrier penetration
https://www.youtube.com/watch?v=X0qgQoej5zE
.380 ACP FMJ fully penetrating 19" of ballistic gel and 8" of water
https://www.youtube.com/watch?v=EkscBbMGp5k
9x19 FMJ fully penetrating 16" of ballistic gel and continuing onward with plenty of energy
https://www.youtube.com/watch?v=mNfp2LtfTHc
.45ACP FMJ fully penetrating 16" of ballistic gel with plenty of leftover energy
https://www.youtube.com/watch?v=3G-txVKnVjY
9x19 FMJ fully penetrating 14" of ballistic gel with plenty of leftover energy
https://www.youtube.com/watch?v=kSrlItrsbvs
5.56x45 M855 FMJ failing to penetrate 16" of ballistic gel, fragmenting violently on impact
https://www.youtube.com/watch?v=HRbAfdoU9vY
5.56x45 XM193 FMJ failing to penetrate 19" of ballistic gel, stopping at 12.5" after fragmenting
https://www.youtube.com/watch?v=RZPGSiDs5_k
5.56x45 XM193 FMJ stopping after roughly 10" and fragmenting violently
https://www.youtube.com/watch?v=6hJZdtPcVdE
5.56x45 M855 fragmenting violently within 5"
https://www.youtube.com/watch?v=SPzxBJSIaGA
5.56x45 V-MAX, a ballstic tip projectile, penetrating only 6" into ballistic gel
https://www.youtube.com/watch?v=aCqmclsRQmM
5.56x45 TAP, law enforcement ammo, violently fragmenting into dozens of pieces after 5"
https://www.youtube.com/watch?v=sukRauELwFk