Minimum headspace for the .223 and 5.56 are the same at 1.4636.
SAAMI drawings shows 1.4636 min and 1.4736 as max for headspace
SAAMI drawings for "cartridge" headspace manufacturing tolerances are 1.4666 to 1.4596
I have seen new cartridge cases .011 shorter than minimum headspace.
I have a .223 Stevens 200 and a AR15 A2 HBAR and load for both, with the sloppy tolerances during cartridge case manufacture of American cases proper fireforming is more important than worrying about setting your headspace tight when you will have cases .007 to .011 shorter than minimum headspace. On top of this how far will the dies you have push the shoulder back when making hard contact with the shell holder. You will have "three" headspace length to worry about and not just the rifles headspace.
Headspace info
http://www.ar15.com/mobile/topic.html?b=3&f=4&t=315921
http://www.ar15.com/forums/t_3_4/487104_.html
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