We could and maybe should have a different thread for this. 5.56 is (generally) loaded a bit hotter. There are 223 spec equivalents of some 5.56 loads and they have a bit less velocity. Almost all 223 and 5.56 loads are boat tail. 5.56 when compared bullet to bullet gets a bit better ballistics just from being a bit faster. The thickness of the metal jacket is irrelevant, even solid copper bullets can be fired safely. The chamber pressure between a 223 and a 5.56 is very similar, well within a safe variation in most rifles.
And you can add to that, most 223 marked semi autos are not actually cut with a 223 chamber, but with a 5.56 chamber. They are marked 223 for legal reasons, some for export, some for import. Some countries don't allow "military calibers" like 5.56, but civilian 223 is safe of course.
5.56 will not blow up a 223 gun, in most cases it will be fine, some it will be hard on the gun, and in some rare cases it may be overpressure enough to back out primers, pierce primers, cause sticky ejection, etc.