.223 vs 5.56?

[DaveN]

Can someone please tell me what if any is the difference between these identical rounds identified with different numbers?
I was asked this question today and I didn't like the answer once it came out of my mouth.
Call it ignorance, doubt or misinformation but I really want the truth.

Thanks

Information

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[LiveFreeOrDie]

US of A standard measurement vs. the rest of the world and the metric system

[jmoore]

There are some differences, but aside from the throat area of the chamber between the two it's all pretty arcane and irrelevant. Just don't use 5,56 in a rifle chambered in .223, especially regarding bolt guns. Most semi-autos are fine to swap. Colts often are marked .223 but in reality are actually 5,56, which doesn't help matters. When you start talking match rifles, there's variations inside variations. Search "Wylde chambering" or similar for an example.

[DaveN]

My Oly Arms AR is 5.56,.223 marked receiver with a 5.56 stamped barrel so I know I'm ok but for someone who ask i'll go by what you said as I know if my life depended on it I'd shoot 5.56 in a .223 semi auto if that's all that was available. thanks

Not to beat a dead horse but is there a difference in pressure IE is 5.56 a hotter round?

[Bulls-I_24]

I have read and heard tons of times...."if it's chambered for .223 don't shoot 5.56". Both my ARs are 5.56 so I never worried about it. I have heard the "extra" pressure in the 5.56 round theory, causing more expansion in the casing resulting in extraction problems but dont quote me

[langss]

http://www.luckygunner.com/labs/5-56-vs-223/ .308 Winchester vs. 7.62x51mm NATO

This should answer any and all questions.

[tower06]

5.56 brass is thicker than .223. As a rule I have always heard ok to use .223 in a 5.56 bore but not the other way around.

[Brian Dick]

I've been interchanging the ammo for 35 years and never had a problem in any weapons system.

[browningautorifle]

I've been interchanging the ammo for 35 years and never had a problem in any weapons system.

I'm with Brian on this. Threads like this are frustrating. We go through them again and again and it never gets solved. And we continue to change 5.56 with .223 ammo in our chambers without incident. Never mind the hot stove league numbers and go shooting...

[jmoore]

I don't think it will ever be a problem with ARs. There's some .223 chambered varmint bolt guns which could be a bit short in the throat for 5.56, but it seems unlikely for any factory rifle newer than 15-20 years old.