10 replies to this topic

[dieselpowered]

So there is quite a bit of confusion over whether or not a .223 is actually a 5.56, or can a weapon chambered .223 fire a 5.56. Well here is some info that should help clear things up. A 5.56 chambered weapon can fire a .223 without issue, where a .223 chambered weapon could potentially have negative results firing a 5.56.

While the 5.56mm NATO and .223 Remington cartridges and chamberings are very similar, they are not identical.

Military cases are generally made from thicker brass than commercial cases; this reduces the powder capacity (an important consideration for handloaders), and the NATO specification allows a higher chamber pressure. NATO EPVAT test barrels made for 5.56mm NATO measure chamber pressure at the case mouth, as opposed to the location used by the United States civil standards organization SAAMI. The piezoelectric sensors or transducers NATO and SAAMI use to conduct the actual pressure measurements also differ. This difference in measurement method accounts for upwards of 137.9 megapascals (20,000 psi) difference in pressure measurements. This means the NATO EPVAT maximum service pressure of 430 megapascals (62,000 psi) for 5.56mm NATO, is reduced by SAAMI to 379.21 megapascals (55,000 psi) for .223 Remington. In contrast to SAAMI, the other main civil standards organization C.I.P. defines the maximum service and proof test pressures of the .223 Remington cartridge equal to the 5.56mm NATO.

The 5.56mm NATO chambering, known as a NATO or mil-spec chamber, has a longer leade, which is the distance between the mouth of the cartridge and the point at which the rifling engages the bullet. The .223 Remington chambering, known as SAAMI chamber, is allowed to have a shorter leade, and is only required to be proof tested to the lower SAAMI chamber pressure. To address these issues, various proprietary chambers exist, such as the Wylde chamber (Rock River Arms) or the ArmaLite chamber, which are designed to handle both 5.56mm NATO and .223 Remington equally well. The dimensions and leade of the .223 Remington minimum C.I.P. chamber also differ from the 5.56mm NATO chamber specification.

Using commercial .223 Remington cartridges in a 5.56mm NATO chambered rifle should work reliably, but generally will not be as accurate as when fired from a .223 Remington chambered gun due to the longer leade. Using 5.56mm NATO mil-spec cartridges (such as the M855) in a .223 Remington chambered rifle can lead to excessive wear and stress on the rifle and even be unsafe, and the SAAMI recommends against the practice. Some commercial rifles marked as ".223 Remington" are in fact suited for 5.56mm NATO, such as many commercial AR-15 variants and the Ruger Mini-14, but the manufacturer should always be consulted to verify that this is acceptable before attempting it, and signs of excessive pressure (such as flattening or gas staining of the primers) should be looked for in the initial testing with 5.56mm NATO ammunition.

Additional information at:

.223 Remington - Wikipedia, the free encyclopedia

[unforgiven5150]

Good info. What I always remember is that a gun chambered in 5.56 can shoot either but a gun chambered in .223 can have issues with 5.56. I just make sure I buy all my ARs chambered in 5.56 and I don't have to worry about.

I have also gotten marginally better accuracy with 5.56, but maybe that's just in head.

[dieselpowered]

Yeah my Colt is chambered in .223 guess that was something I did not think about when I got it.

[unforgiven5150]

Do some internet searching but I seem to remember somewhere that Colt labeled some of their stuff .223 but would handle 5.56.

[dieselpowered]

Interesting, I will look around.

Guess I could also call Colt and ask them.

[CBR_Rob]

I have also gotten marginally better accuracy with 5.56, but maybe that's just in head.

I started shooting 5.56 in my bushmaster and have noticed better accuracy. This is good info too. I have been wanting to get into reloading and was unsure if I could load .223 and 5.56 cases the same. Now it looks like a negative on that.

[Rubber Duck]

I notice a little better accuracy using 5.56 in my Bushmaster but can buy .223 Rem for less money and when shooting in the dirt, I can't justify spending more for the 5.56 ammo.

[CBR_Rob]

Check out ammo to go.com I got a great deal on some 65 gr 5.56. Actually better deal than any brass cased .223 than I could find at the time.

[John Kuhns]

_{Guys, there are lots of places to buy 1x GI surplus brass. Of the thousands of rounds fired in competition or practice I've yet to fire a single round of factory ammo.}

Edited by John Kuhns, 30 December 2011 - 09:23 PM.

[Kevinjs1]

1x brass is cool, but I still don't do my own reloading. Are you in the business of reloading for sale???

[John Kuhns]

1x brass is cool, but I still don't do my own reloading. Are you in the business of reloading for sale???

No, I am not. Sorry.