From the linked article.
5.56 NATO is NOT .223 Remington. Although nearly identical in outside dimensions they should be treated as different cartridges. You can shoot .223 Rem in a NATO chamber, but it will expand to fit the looser chamber, and will not give premium accuracy. Unfired 5.56 NATO brass will “fit” into a .223 Rem chamber, but NATO ammo is loaded to higher pressures, making it unsafe, or at the least, uncertain in it’s pressures, to properly operate in a tight SAAMI .223 Remington chamber
Let me get this straight.
The 223 and the 5.56 have identical outside dimensions.
The chamber of the 5.56 "is" looser than the 223.
Shooting 223 ammo in a 5.56 will be inaccurate due to the loose chamber.
5.56 ammo will physically fit into a 223 chamber (same size).
If this logic holds true then firing 5.56 ammo in a 5.56 chamber will be "Inaccurate" as the outside dimensions of the ammo are identical and it will have to expand to fit the loose chamber as well. Hogwash.
Take this logic to the reloading bench.
There is no such thing as a 5.56 sizing die.
Loading for a 5.56 chamber will require a 223 Rem die.
According to this article, handloads for the 5.56 will not be accurate due to cases expanding in the loose chamber. More Hogwash.
As you can see here the difference between the 223 and the 5.56 chambers is in the throat area not in the case body. Compare the PTG 223 to the PTG 5.56. Then tell me that the chamber bodies of the 5.56 are "looser".