What are the differences .223 vs 5.56?

[ar15barrels]

I'll throw my two cents in...

http://ar15barrels.com/data/223-556.pdf

Someone mentioned brass being thicker on the 5.56 and I have data that says it's not:

http://ar15barrels.com/data/223weights.xls

[Fjold]

so do the same rules apply to .308 vs 7.62?

There are headspace differences between the two rounds. The .308 go-gauge is 1.6300, the .308 no go-gauge is 1.6340. The 7.62 go-gauge is 1.6350, the 7.62 no go-gauge is 1.6405. Since NATO military ammunition can come from any NATO country, and the goal is the ability to interchange ammunition, the military chamber is larger.

The 7.62 Nato is loaded to 50,000 PSI and the SAAMI spec for 308 Win is 62,000 PSI.