How do you know if the chamber is 5.56 or .223

[imschur]

A friend recently traded for an AR-15. The barrel is not marked as to the caliber and the manufacturer "thinks" its a 5.56. Is there an easy way to verify the caliber?

[98Z5V]

The difference is in the leade - distance from case mouth to where the rifling start in the barrel.  I've got the numbers buried in my computer somewhere, so I'll try to find them.  I've got tons of articles saved on the differences between the .223 Rem ammunition versus the 5.56mm NATO ammunition, and the exact measurements are listed in one of those articles.  Wading through them will take me a little bit.  Hopefully, somebody beats me to this one...  <laughs> <thumbsup>

Another factor to consider for chambers is the .223 Wylde.  It's a hybrid between .223 Rem and 5.56 NATO measurements/differences.  It's the "all-around" chamber; safe for 5.56 pressures, shoots both, more accurate than both.

Be advised - to measure the differences in the leades, you'll need some precision measuring gear.  I'm not even sure a "standard" 6" digital caliper (with depth gauge) would be sufficient to get into the chamber, from the back of the upper receiver.  <dontknow>

EDIT - the barrel should be marked somewhere - most obvious place is in front of the front sight post location / gas block location.  If it's not there (obviously not, in this case), have him look under the handguards somewhere.  I know for a fact that Colt puts some of their barrel-specific markings under the handguards (date stamp of production for the 14.5" heavy SOCOM barrels is under the guards).

[imschur]

The only marks on the barrel are M1S so Im not surprised it isnt marked. They told him "its probably 5.56"

[bandit10-4]

All of the M1S barrels Ive ever seen were marked 223 if 223 and if not marked were 5.56, so Id say 99% sure its 5.56.  If you want to be 100% sure you can take a case and cut the neck with a dremel long ways so you can put a bullet in it by hand tight, then chamber it gently. extract gently and then measure, then do the same in a standard 223 chamber and compare. 

[imschur]

thanks guys

[Madhouse]

I guess I always assumed any quality mil-spec AR would be chambered in 5.56x45, maybe that's not such a safe assumption...

<dontknow>

[imschur]

I guess I always assumed any quality mil-spec AR would be chambered in 5.56x45, maybe that's not such a safe assumption...

<dontknow>

Many companies offer both. Supposedly the .223 gets the nod for accuracy. i wonder why they dont all standardize on the Wylde chamber  <dontknow>

[98Z5V]

Found it - took some digging.  :o    Original Poster of this info (made the diagram) is chris65 from another message board - just giving proper credit, 'cause it's a good chart.  <thumbsup>

This is .223 Rem, 5.56mm NATO, and .223 Wylde compared.  Chamber dimensions are based off the chamber reaming tools.

[imschur]

thanks buddy