223 and 556
Here it is!
the important difference is the lethality difference- the .223 is only capable of killing small game animals and such while the 5.56mm cartridge is fully capable of downing passenger jets owing to the fact that it is commonly fired from an AR15. If the 5.56 round is fired from a wood stocked mini-14, its letahlity is reduced to that of the .223 round however.