.223 Remington vs. 5.56 x 45mm NATO

[Midnight Raver]

Given the previous topic of discussion on military/civilian round compatibility, I figured on bringing this one up. Plenty of you comsume this stuff in your firing pieces on a regular basis, that is for certain! So, are the two different rounds normally interchangable or is there a marked difference between them?

 

[11B3XCIB]

The rounds are not normally interchangeable unless you have a 5.56mm NATO rifle. If your rifle is chambered for .223 REM, it's recommended that you do not fire 5.56mm NATO from it. A .223REM rifle will chamber a 5.56mm round no problem, and vice versa, but the .223 REM chamber isn't made for it.

Difference in brass
On a 5.56mm NATO round, there is usually a + sign with a circle around it. This is an obvious marking difference, and the .223 REM will probably be stamped as such near the primer. If there is any internal difference in either brass, I don't know...I don't reload it and I don't shoot .223 REM, only 5.56mm NATO.

Difference in Chamber
The difference between the .223 REM and 5.56mm NATO chambers are in the throat.This is the part of the barrel directly in front of the chamber where there is no rifling to allow space for the seated round. The throat in a .223 REM chamber is a tighter spec while the throat in the 5.56mm chamber is a little wider. We're talking hundredths and thousandths of inches, though. I don't know the exact numbers off the top of my head. But, the added space in the 5.56mm chamber compensates for the added pressure inherent in the 5.56mm NATO round. This is where you have problems chambering a 5.56mm round in a chamber designed for .223 REM: this can potentially create an over-pressure situation outside of the chamber's tolerance. I'm sure there are a bunch of people that have fired 5.56mm NATO in a rifle designed for .223 REM with no problems, but if it's against the manufacturer's recommendations and something goes wrong with the rifle (even if it's not related directly to the ammo) good luck getting them to pay for it. I've never seen a .223 REM rifle destroyed by using 5.56mm in it, but I would not be willing to change it with my eyes/face/hands/fingers, etc.


To me, 5.56mm NATO is like a .357 round, and .223 REM is like a .38 Special. The rounds can be interchanged due to the size, and a .38 revolver will probably tolerate .357 rounds for a while, but you don't want to be the one holding it if it ever fails.

 

[bigfutz]

Chamber pressure goes the other way on 308/7.62 though. The 308 cartridges are hotter. viewtopic.php?f=12&t=3184

The hotness is where I've heard the most arguements WRT 223/5.56, but it seems case dimensions/chamber fit is a more predominant issue with 308/7.62.

 

[Tigerstripe]

Chamber pressure goes the other way on 308/7.62 though. The 308 cartridges are hotter. viewtopic.php?f=12&t=3184

The hotness is where I've heard the most arguements WRT 223/5.56, but it seems case dimensions/chamber fit is a more predominant issue with 308/7.62.

so when reloading 223 and 5.56 if you dont get near max loads, in an AR (5.56) it wont make any difference. i have no 223 rifles so i dont make a distinction reloading. right? wrong?

 

[bigfutz]

Chamber pressure goes the other way on 308/7.62 though. The 308 cartridges are hotter. viewtopic.php?f=12&t=3184

The hotness is where I've heard the most arguements WRT 223/5.56, but it seems case dimensions/chamber fit is a more predominant issue with 308/7.62.

so when reloading 223 and 5.56 if you dont get near max loads, in an AR (5.56) it wont make any difference. i have no 223 rifles so i dont make a distinction reloading. right? wrong?

All sources are pretty much in agreement it's OK to shoot 223 in a 5.56 but not the other way around, unless you are rolling your own you can do what you want.

 

[biganimal]

I shoot both in my rifle marked 5.56 and the other one that is marked .223
BUT
I haven't shot factory ammo thru either EVER!
all my ammo is hand rolled and always under max loads so pressure is not a problem