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The Difference Between 5.56 & .223

Posted by Kris Vermillion on February 4, 2019
Posted in: Ammo
What is the difference between the 556 and 223 rounds?

The factors that separate the 5.56 NATO round from the .223 Remington are so small yet so significant.

They provide countless hours of conversation on gun counters and internet forums, and if misunderstood, they could provide a really bad day on the range.

So what are the differences between 5.56 NATO and .223 Remington, and can you own one rifle and shoot both?

This article will clear it all up for you right here, right now.

TL/DR: Can you shoot .223 Remington out of a 5.56 NATO? Yes.

Can you shoot 5.56 NATO out of a .223 Remington? No.

The difference that matters most is the fact that the design of the 5.56 NATO round and the chamber results in a higher pressure than the .223 Remington round.

Knowing the original intent of the 5.56 NATO round gives some insight as to why it was (and is) built the way it was (and is).

American Rifleman says:

"The 5.56x45 mm surfaced in 1957 as an experimental cartridge in the AR-15 rifle. The concept was to develop a smaller, lighter military cartridge that would still be traveling faster than the speed of sound at 500 yards, and this was accomplished by using a 55-gr. boat-tail bullet. The AR-15 evolved into the select-fire M16 rifle that was adopted by the military in 1964.

Remington was quick to act, and very shortly after the military adopted the 5.56x 45 mm cartridge the firm brought out the civilian version, called the .223 Remington."

If you can remember that 5.56 NATO was made for the military while .223 Remington was designed for the civilian market, and you're good at memory by association, now is a great time to make this point: You can shoot 5.56 NATO AND .223 Remington out of a 5.56 NATO Chambered rifle, but you CANNOT shoot 5.56 NATO out of a .223 Remington chambered rifle.

Think of it this way: A "military rifle" (remember where 5.56 NATO came from) will shoot a "civilian bullet" (remember where .223 Remington came from), but a "civilian rifle" would never be strong enough to handle a "military-grade bullet". There's a lot of quotation marks and parentheses in there because that phrase is not to be interpreted literally but only to serve as an easy way to remember the very important difference between 5.56 NATO and .223 Remington.

The higher pressure of the round is the result of design differences between the 5.56 and .223 respective cases. There are subtle dimensional differences in the cases of the rounds and the throats of the barrels (known as the leade) made for each respective round.

From Shooting Illustrated:

"That chamber dimension for the 5.56 NATO is, in fact, slightly larger than the chamber for the .223 Rem.'in order to have the smoothest feeding and ejection, even with a dirty weapon, to best serve as a battlefield implement but it is the leade dimension that makes the biggest difference. Leade is defined as the area from the bullet's resting place before firing to the point where the rifling is engaged. The shorter the leade dimension, the faster the bullet will engage the rifling, and the faster the pressures can rise to a dangerous level.

In a nutshell, the 5.56 NATO has by design almost twice the leade that the .223 Remington does. So, a cartridge designed for a long bullet jump, or leade, which is fired out of a chamber with a shorter leade as is the case when firing 5.56 NATO ammunition out of a .223 Rem. The chamber can result in a fast and dangerous pressure spike. Again, firing lower pressure .223 Rem. ammo from a 5.56 NATO chamber is no issue, but firing higher pressure 5.56 NATO ammo from a .223 Remington chamber es no Bueno...the military 5.56 NATO case will tend to have thicker walls, resulting in less case capacity, and correlatively higher pressure, if the same powder charge is used. If the exterior dimensions are identical, a thicker wall dimension must result in a smaller interior volume."

Hopefully, you now feel well-informed on the topic of 5.56 versus .223. Share this artic le if you think it will help someone else cut through the weeds. And if you need to re-supply your own cache of either the 5.56 NATO or .223 Remington round, please refer to our main Ammo page. Also, be sure to check out our large selection of traditional .223 Rem rifles and 5.56 rifles as well as AR-15 rifles chambered in 5.56 and .223

4 years ago at 1:14 PM
I know it would lead to some confusion on the subject, but could you include some information on the 223 Wylde chambering?
Dion White
4 years ago at 12:14 AM
223 Wild has better tolerances for both the two to three and five five six round. From a headspace issue. It just helps with the chambering
T.C. Brooks
4 years ago at 12:52 AM
Simply means that you can use either cartridge . 223 Rem. or 5.56 Nato
Tom Scott
4 years ago at 2:36 PM
The statement about a civilian rifle not standing up to a military grade cartridge only holds true for 5.56x45. The 308 Win is a higher pressure round than the 7.62x51 Nato cartridge therefore the whole concept is reversed. You can shoot a 7.62 Nato round in a 308 but not safe to shoot 308 in a military chambered 7.62.
Todd Koeppel
4 years ago at 4:45 PM
The same could be said for .30-06. It is not advisable to shoot civilian .30-06 from your M1-Garand due to the increased pressures in the civilian loads as opposed to the military version.
pc macdonald
4 years ago at 2:46 AM
This is not due to increased pressures. This is due to a longer pressure profile moving the pressure peak from early to late down the barrel, over pressuring the gas system and often tweaking the op rod.
4 years ago at 4:43 PM
Why didn't the author bring up the shoulder angle difference which is obvious in the pictures. Pressure may be an issue, but stove piping a 5.56 in a .223 chamber, to me, has always been the bigger problem. Side by side pressures comparisons aren't the big of a difference with factory charges. That's why the Dylan chamber came about, splitting the shoulder angle differences. .308 Win has higher pressure than 7.62 NATO. The NATO cases of both 5.56 & 7.62 have steeper shoulder angles and that moves leads of jump.
4 years ago at 4:44 PM
*Wylan chamber* damn sp check
pc macdonald
4 years ago at 2:46 AM
errr..... \"WYLDE\" chamber.
4 years ago at 7:29 PM
There is no shoulder angle difference between the two cases. They are for all intent purposes identical.
Tom Scott
4 years ago at 7:58 PM
There is absolutely no difference in outside dimensions between the two cases. Not in 5.56 vs 223 or 762x51 vs 308. Exact same dimensions. And it is not a Wylan chamber, it is Wylde.
4 years ago at 7:19 PM
Am i the only person reading this in the voice of gunny?
PAMAX Tactical
4 years ago at 10:50 PM
This article muddies the waters. It holds true to old manufacturing but now almost all .223 barrels are .223 Wylde. Barrel Markings .223 Wylde = 5.56 Nato and .223cal 5.56 Nato = 5.56 Nato and .223cal .223 or .223 Only = .223cal
pc macdonald
4 years ago at 2:47 AM
'Taint so. WYLDE is common, sure. And you won't find one in a bolt gun.
Kat Clark
4 years ago at 9:25 PM
Makes me glad my M4 A3 was chambered for 5.56 nato.
4 years ago at 6:19 PM
If using 556 brass but loading to 223 load specs will there be a problem with use in a 223 because of pressuse due to smaller case capacity ? Thanks
Lee Samuelson
4 years ago at 3:03 AM
4 years ago at 10:59 PM
So, I'm assuming that I can use a shell marked 5.56 when I reload to 223.
4 years ago at 2:36 AM
Yes you Can use 5.56 brass, but you must run the 5.56 thru a full length 223 resizing die, then trim the shell to proper length, and you are ready to reload. If you do not follow this process, the cartridge will not fit in a 223 chamber. If you full length resize you should be able to use it in either 5.56 or 223. Chamber
4 years ago at 7:46 PM
In the second picture down from the top the labeling seems to be reversed. From other articles I have read, the 5.56 has the crimp ring that the .223 does not.
T.C. Brooks
4 years ago at 6:57 PM
Bought a Savage Axis II in Troy Al. about two mos. ago . The problem I had was 2 out of every 10 rounds might fire. The problem area is in the bolt body. Savage uses a molded washer around the forward end of the firing pin and inside the bolt body drag between this washer and the wall of the bolt body occurs resulting in a light primer strike. I did some polishing and clearance work in this area and haven't had a light primer strike since . In ref to the .223 Rem & 5.56 diff. I have a savage bolt gun in .223 Rem and it has such a long leade that it is longer than the military 5.56 chamber in the AR 15 /16 rifle ! A shooter needs to know this before firing his or her non military rifle rifle .
4 years ago at 11:28 PM
I disagree. A few decades ago this article may have been accurate, but not today. While SAAMI specs may indicate different maximum pressures, the EU doesn't recognize SAAMI and has a different standard. In the EU specs, if a firearm can chamber a round, it must be engineered to the maximum pressures possible for the round. All .223 rifles will chamber a 5.56, and no manufacturer is going to exclude their product from the European (NATO) market. Therefore all manufacturers will engineer to the higher pressure possibility. In addition to that, pressures will vary depending upon the weight of the bullet. All engineering will be done to heaviest bullet weights in order to reduce liability. I'll continue to have complete confidence in modern firearms chambering and safely firing both rounds. For older firearms, certainly pre 2k, caution may be prudent.
Michael Gilbert
4 years ago at 10:14 PM
Thank goodness some sanity came through. I have found by tickling max load data and creating leade differences have frequently created better accuracy. I've never encountered any pressure signs from this practice or shooting 5.56 in a .223 chamber. I just wish the industry would all have presence of thought and good design to standardize at 1 to 7 twist to get the most out of these firearms. \"Only accurate firearms are interesting.\"
Fred Colantuoni
3 years ago at 6:44 PM
I was in the Army Infantry in Vietnam. I wonder why all the ammo issued to us for the M16 was marked both 5.56 and .223?
M. Cantera
3 years ago at 11:20 PM
At that time there was only one specification: MIL-C-9963, MILITARY SPECIFICATION: CARTRIDGE, 5.56MM, BALL, M193 The M193 as the the same as the same as the civilian cartridge. A 55 grain projectile loaded to 55,000 psi. The whole silliness came about as the result of the NATO trials, which required the penetration of a Soviet helmet at 400 meters. The Belgians came up with a 5.56 SS109 62 grain steel tipped round loaded to a higher pressure. That was adopted as the M885 \"green tip\" of today.
Patrick Kennedy
3 years ago at 10:47 PM
See spellz checks hates youz too. I thunk it was only me!
Patrick Kennedy
3 years ago at 11:06 PM
A Mil Spec 5.56 case has less internal volume than a 223 Rem. If you do a water volume test you will see. Same on 7.62 vs 308. Mil Spec 30-06 vs civilian brass, same thing. Mil Spec brass is stronger and thicker near the back of the case thus decreasing the volume. Load a Mil Spec case to max civilian pressures and you are at a unsafe pressure. One sees this when modifying 5.56 to 300 Blk Out. The crimp in the Mil Spec case is to keep the primer in the case during rapid/full auto fire and the thicker back of the case is to keep brass rupture out of the picture. A full auto stops real fast when a primer pops out. The upside of the smaller case volume is that less powder causes the same velocities as compared to civilian brass. Patrick (I am not an old know-it-all but I portray one in real life, so says,my wife.)
zack p vandyke III
3 years ago at 7:43 PM
Absolutely, totally correct!!!!
Philip J Broome
3 years ago at 4:27 AM
I think all these guys like to hear themselves talk.. lol But I do find it interesting
Robert Lee Wood
6 months ago at 4:29 PM
The round given to me for the weapon does not look like either, I was told it was a 5.56 round but it is a shorter fatter round on the end without the beveling down at the end