5.56mm NATO versus 223 Remington Chamber Differences

[mike_556]

Awesome and informative post Molon!!

[BlackRifleMedic577]

New to the site. Good thread!! Thanks for the info.

[hunt_ak]

Tagged....

Thanks, Molon!!

[donwalk]

also...one should keep in mind that once fired in a 5.56 chamber, the .223 is 'fire-formed' to the 5.56. that in turn alters the water capacity of the case...ever so slightly, but the brass should be kept separate for re-loading purposes.

different primers and a 'hot' load could result in a spike in pressure.

[markm]

also...one should keep in mind that once fired in a 5.56 chamber, the .223 is 'fire-formed' to the 5.56. that in turn alters the water capacity of the case...ever so slightly, but the brass should be kept separate for re-loading purposes.

different primers and a 'hot' load could result in a spike in pressure.

Huh? Chamber dimensions are THE SAME. The cases don't touch the leade which is where the two differ.

[donwalk]

i saw an article and diagram, where the case shoulders differ slightly in angle.

at the moment i cannot recall...i will research the article and see if i can recover it. (the article)

[markm]

Ok. I was just looking at the pic above where it says chamber dimensions are the same. I'd think that a resizing die is going to bring the brass back to the same size regardless though.

[slomo]

If the only difference between 5.56 Nato and .223 Rem chamber is the leade and freebore then why is the allowable headspace greater with 5.56 Nato?

[markm]

If the only difference between 5.56 Nato and .223 Rem chamber is the leade and freebore then why is the allowable headspace greater with 5.56 Nato?

You mean "allowable" before the bolt or barrel gets replaced?

[slomo]

Yes. According to the data I've seen No go for .223 Rem is 1.4666" and No go for 5.56 is 1.4736". Why the difference if the cases of .223 and 5.56 are the same dimension from the cartridge base to shoulder.

For instance, if I mounted a new barrel labeled .223 Rem and the bolt would close on a No go 1.4666" gauge the bolt/barrel headspace would be out of spec. but would not be out of spec if it were a 5.56 Nato chamber.