Okay I know this is an idiot question but.

[HBARleatherneck]

what docmedic said. the wylde chamber is tight

i can shoot wolf through all 4 or my other ars.

i can not shoot wolf through a RRA HBAR upper chambered in .223 Wylde

i can, but it doesnt extract reliably (read bolt face stuck in chamber)

i know some of you are too good to shoot wolf and question why I am shooting it, but its cheap. I load my own ammo, but sometimes I just shoot it.

[Hoosier]

My AR doesn't have a clear label on the barrel, but it will only properly cycle M855 NATO 5.56 ammo, every .223 round FTE or the next round fails to chamber.

H.

[Daniel_187]

I have some once fired brass .223 and 5.56 and messured them with the cailipers and the 5.56 was a little bit longer the .223

[HBARleatherneck]

that is common.

from one manufacturer to another
from one lot to another
from one powder charge to another.

the cases grow at different rates.

[DD977GM2]

Here is a great source for anything related to 5.56 NATO or .223 ammo.

http://ammo.ar15.com/ammo/


As much as I can not stand the site, it still has its atributes for learning just about anything firearm related, especially ANYTHING for the AR15 platform.
FWIW, this is not a stupid question. It is a common question that I even have to reference from time to time as my memory sucks donkeyballs.

[cleaner72]

Scratchy is correct.

There are pressure considerations that can get you into trouble.

In a gun chambered for 5.56mm, you can shoot both 5.56 & .223
In a gun chambered for .223, you can ONLY shoot .223.

Everyone knows someone who says that they shoot 5.56 and .223 interchangably in any .223 rifle. While you might just get away with doing this for a while, it would be nothing short of playing roulette - it might be the first round or the 50th that blows the gun apart and takes your hands and face with it.

Ginsue is correct its all about the pressures..... 5.56 will take both .223 only in a .223

[SA Friday]

OK, here's a monkey wrench it everything for you all: Why? The 5.56 chamber actually has a little less metal around it in comparison to the 223 if the specs chart attached is correct. All barrels in an AR fit in the upper at the same diameter, right? The rounds can only be loaded to a certain length as the mag is the limiting factor for OAL in both chambers. So, the amount of pressure difference can't be all that much; 5,000 PSI maybe? So, which factory is loading 60,000 PSI 223 or 5.56 ammo? I don't know of any pushing the limits that hard with any bullet weight, not even nato. 223 and 5.56 will both chamber in each other's chambers with full bolt lock-up.

So... I don't get it. SAAMI sets standards, but that doesn't mean the standards are completely correct as they have to set the standards for the lowest common denominator. 45LC and 45-70 are both great indicators of this. You can load 45LC to surpass 44 Mag ballistics if shot out of a Ruger, but the same will kaboom another gun made to the black bowder specs. Has anyone actually seen (don't want to hear you read it in a blog this one time on AR-15 dot com...) an AR kaboom from this? No other reason it could have kaboomed? I have to ask as I've been shooting 15's and 16's since I was 11 and have yet to actually see one blow from using 5.56 in a 223 chamber in an AR, and bro, I shoot quite a bit. I could see how this might be an issue in a Mini 14 or bolt gun, but an AR? Na, I just don't see it happening.

I'm open on this one. I could be disuaded from my position, but you better have some good evidence/bonafides to change my opinion on this one.