TO ME.......it boils down to this.
* A 5.56 chamber has more throat/leede/freebore.
* A 5.56 throat is wider
* Some military loadings are loaded to a higher pressure.
* A 223 fired in a 5.56 chamber is completely safe but usually,kinda,fairly,semi,inaccurate.
* A 5.56 that is chambered in a 223 chamber sometimes has some bullet pull if they are not crimped.
* Sometimes you will find indications of over pressure if a 5.56 is fired in a 223 chamber.
* Sometimes you will find indications of a headspace problem if either is fired in the others chamber.
* Most all CIVILIAN 223 and 5.56 marked ammo is interchangeable.
* ALL 223 and/or 5.56 chambers are different.
* Most all ammo is different.
* The above does not always hold true....your experiences may vary.