One of many citations from
this source compared 9mm, 10mm, and .40 calibers and then concluded “In every test, with the exception of soft body armor, which none of the SMG fired rounds defeated, the .223 penetrated less on average than any of the pistol bullets."
This is desperate.
You're talking about penetrating drywall. Gethsemani is talking about penetrating human bodes.
The actual tests clearly show that the
relative lack of penetration of successive layers of drywall/insulation with .223 is due to tumbling. Tumbling is actually an intentional part of the design of .223 rounds. Upon impact, the bullet deforms slightly causing it to spin or "tumble" inside the target, inflicting more tissue damage. Obviously, bullets are not designed to fly through air while tumbling, so the fact that it doesn't retain the same ballistic properties after penetrating multiple walls separated by air gaps shouldn't surprise anyone. A human body, however, is just a single mass.
Another consequence of tumbling, which you can actually see clearly in the examples given, is that the bullet's trajectory deviates after penetrating. In some of the examples, it doesn't even hit the rear layers of drywall because its trajectory has curved. This means that it's actually impossible to know exactly where the bullet will end up after penetrating, which is
a very good reason why you shouldn't fire it into a crowd.
The FBI and "professional door kickers" (whatever that means) adopting .223 ammo has basically nothing to do with overpenetration. It's about stopping power. In particular, the FBI's experiences in cases like
this one have generally illustrated the fact that handguns don't incapacitate people quickly enough due to low muzzle velocity and a lack of penetration.
A .223 rifle has a muzzle velocity close to a kilometer per second, compared to a 9mm handgun which typically manages about 300m/s. That's why it's a jacketed round, because lead alone would shear at that velocity and potentially damage the barrel of the gun. That velocity translates into more penetration into a human body than a pistol round, which means more tissue damage and more chance of incapacitating someone. That penetration is the desired effect and the main advantage of using a higher velocity round.
But if you won't listen to me on this, lemme just quote the part of your link that actually matters.
The bottom line to remember in all of this though is to still be aware of your target and what is around/beyond it because ALL bullets that will penetrate deep enough to stop an attacker will still penetrate at least one interior wall. And even a bullet, like the .223 that tends to lose steam and deviate after a wall or two can still be deadly to your family/innocents.
