Sheesh. Y'all should be ashamed you can't bother to do a little research:
1) The Google is your friend, i.e. Lucky Gunner's Lab
5.56 in .223. This has been wondered, and answered, innumerable times.
2) The different in published loading data between 5.56 and .223 is on the order of 3-5% charge weight.
3) The brass and primers are the same within normal inter-manufacturer variation, and LC brass is some of the lighter (thinner) brass available. If 5.56 produced pressures more than a few % above .223, the brass would have been redesigned.
That picture posted above (pretty disingenuously) is of a catastrophic over-pressure event, likely an obstructed bore, possibly a wrong-powder reload. 5.56 in a .223 chamber leade will result in over pressure on the order of 10% (see Lucky Labs above). At the
very worst, you might experience a pierced primer or hard extraction. I never have, and I've run a fair bit of NATO surplus 5.56 through my .223 bolt gun, as have thousands of others.