I've seen various threads here about the advantages of a 5.56 chambering vs .223 REM, and the dangers of using 5.56 military ammo in a .223 chamber. On that same thought, there have been a few threads talking about how some chambers may be mis-marked,  or a lower could be marked one thing and connected to an upper that is not the same as what's marked on the lower. So, I was wondering is there anyway of telling what a chamber is for sure? measurements to take or the like?

I mean, in doubt it would always be safer to just shoot .223, but if you had a 5.56 chamber, why not make use of it?

No Expert

The 5.56 chamber is the "looser" chamber, to allow for slight differences in NATO ammo, and to give slightly greater tolerances for increased reliability. The 223 rem chamber is a tighter chamber, which gives better accuracy with 223 rem ammo, but might or might not work well with all 5.56 ammo (223 ammo will function fine in 5.56 chambers).

The calibre marked on the lower receiver is does NOT tell you what the barrel chamber actually is, since lowers and uppers are easily changed (because of this, some new lower receivers do not indicate calibre). The upper reveiver, of course, has no calibre markings at all.

Only the calibre marked on the barrel tells you what the true chambre is. It could be mismarked, but I would guess that this is very rare. The only way to know for sure would be to use chamber guages.

okay, so it would be a set of Go & No-Go guages for .223 & 5.56 that would be needed to verify a true chamber spec.  I had looked in troubleshooting...but would have nevber thought to look in the thread on "blown primers".

Thanks,

No Expert

Well, according to the "Nosler Reloading Manual, 5th Edition", the difference between .223 and 5.56 is a mil spec (ie. 5.56) cartridge is made with a thicker wall than a .223, causeing higher pressure with the same amount of powder...  

-Jbot

Thanks for the detailed info, Tweak. I stand corrected on the headspace gauges.

Now for the differences in "Chamber Gauges" mentioned above that Tweak already correctly referenced as Headspace gauges.
Tweak and I compiled this:

www.ar15barrels.com/data/headspace.pdf

You can get the original PDF file of that chamber reamer comparisons page on my tech page along with lots of other boringly technical stuff.

Randall Rausch
www.ar15barrels.com

Wow.... information overload

But, there is still no way of knowing what chamber one has for certainty without casting it?

Okay, easiest way to do that is????

No Expert

Quoted: But, there is still no way of knowing what chamber one has for certainty without casting it? Okay, easiest way to do that is????

Brownells Cerrosafe

Randall

Try dental impression paste.
www.ar15.com/forums/topic.html?b=3&f=4&t=250631

You won't have to heat anything but dinner!