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223 and 5.56 "chambers" are for all intents identical, (and so are the pressures -- SAAMI v CIP measurement differences notwithstanding)
The throat leade ahead of the neck on the 5.56 may be a bit longer, but the case never sees that at all.
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If one fires 5.56 in a barrel chambered for .223 the shorter throat produces higher pressure - which, with steel cased ammo, allows gas and particles to blow past the case neck and shoulder before the case expands to seal the chamber. This grit builds up with each shot to the point where it grabs hold of the polymer or lacquer coating on the case and sticks the case to the chamber.