Featured Is There a Difference Between .223 and 5.56? - TheArmsGuide.com

Published on March 4th, 2013 | by Destinee (FateofDestinee)

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Is There a Difference Between .223 and 5.56?

The comparison between .223 and 5.56 isn’t a new one, so there is a lot of discussion to weed through to learn about the two. Ultimately, because they originated from the same cartridge, they are very similar, but that does not mean that they are necessarily interchangeable. This article discusses three key differences between .223 Remington and 5.56x45mm NATO.

.223 Remington and 5.56x45mm Dimension Measurements

At a glance, the two rounds are indiscernible. Both rounds use a bullet of .224in in diameter and an overall length of 2.26in. In general, the external dimensions for the two calibers are identical. What’s more significant is the pressure of the two rounds and the difference in the rifle chambering.

.223 Remington and 5.56×45 Pressure Measurements

One of the problems with comparing these two cartridges is that they utilize different methods of measuring pressure. SAAMI (Sporting Arms and Ammunition Manufacturers’ Institute) measures the .223 pressure at the center of the casing, whereas the NATO standard measures the pressure at the throat (or leade) of the chamber. To rectify the two different methods, several have undertaken experiments with their own standardized recording method to compare “apples to apples.” One such thorough study was carried out and recorded in detail by Andrew Tuohy posted via Lucky Gunner Labs (click here to read the full article). Tuohy evaluated various .223 and 5.56 ammo fired through rifles chambered for .223 Remington and 5.56x45mm.

His, and the research of others, confirms that, generally, shooting .223 through a 5.56 chamber results in lower pressure, but still functions (safely). Firing 5.56 through a .223 chamber, however, results in somewhat higher pressures. Although the differences aren’t massive (~5% in the previously referenced study), extensive firing of 5.56 through a .223 chamber could lead to over-pressure malfunctions, such as popped primers or blown cartridge case heads and other firearm malfunctions.

.223 Remington and 5.56×45 Chamber Differences

The most important difference between .223 and 5.56 chambers is the length of the throat (or leade) for each chamber. More specifically, the leade is located at the mouth of the barrel before the rifling occurs. Comparing the NATO and SAAMI regulations, the leade for 5.56 chambers is nearly twice as long as that of a .223 chamber (.162in to .085in, respectively). If a 5.56 round contacts the barrel rifling too early, it can cause pressure spikes (leading to malfunction, and potentially damage) in the chamber. This explains why it is safe to fire .223 through a 5.56 chamber, but not recommended to fire 5.56 through a .223 chamber.

Is There a Difference Between .223 and 5.56? - TheArmsGuide.com

Bruce (my first AR15) is chambered for 5.56x45mm NATO.

Which should you choose?

As with so many elements of making a firearm purchase, the “right” option is subjective. If all you intend to purchase are .223 Remington rounds, there is nothing wrong with getting a rifle chambered for .223. However, if you want the option of firing milspec 5.56 through your rifle, you may prefer picking up a 5.56 chambered rifle. After all, you can still fire the .223 through it, safely, if you want. Price and personal preference are also factors to consider when making that decision. What works for you?

Featured images of Remington UMC and WInchester M855 ammos courtesy of midwayusa.com

About the Author

In addition to writing for The Arms Guide and her personal blog, Destinee is also a vlogger. She publishes videos on weapons, gear, and fitness on her YouTube channel every Tuesday and Thursday.


55 comments
KathyCat
KathyCat

Maybe somebody can help me, I just bought my first AR 15 or whatever and it says on the barrel 5.56 and I haven't been able to find bullets that just say 56 but I did find some that did say 5.56 but I can't get 5 of them in the barrel at the same time, I put one in the hole where the bullet goes and then try and put the second one in there and it doesn't seem to fit so I hit the charge handle thing real hard trying to force the second one in and it fires one time every damn time and I almost shot my foot off the first try so before I try it again how the hell do you get 5 of these 56 bullets in the barrel at the same time?

BerettaPX41958
BerettaPX41958

@KathyCat Take your rifle back to whoever sold it to you and get your money back. You are too stupid to own a firearm. 

EJWyssJr
EJWyssJr

I'm beginning to believe that the difference between the two cartridges is that the .223 Remington is the 55 grain projectile M-193, and that the 5.56mm NATO is the 62 grain projectile SS-109/M-855.  That and the military's specifications to the chamber dimensions. 

RoyTaylor
RoyTaylor

In 1971 I Captured Two VietCong armed with civilian modal AR 15s and .223 Ammo, which can be fired from any 5.56 Simi Automatic Only. Attempting to Shoot .223 ammo On Fully Automatic Mode Military M16 ,can cause your AR15M16 to jam OR Explode in your face

EJWyssJr
EJWyssJr

@RoyTaylor  What you captured were probably a couple of ex-ARVN Colt 601s or 602s (early M-16s).  I carried some early M-16s with XM-148s attached to the barrel as a Security Policeman in the USAF at Clark AB RP in 1988-1990.  The early rifles had nothing stamped on them about being and M-16 they were just stamped AR-15, the caliber was stamped .223 Remington.  To tell if it is an early rifle it will have a slick sided right side of the lower receiver, it will not have a protective fence around the mag release, nor the raised surface above it.  The bolt hold open device will lack the raised nipple of later rifles and the upper receiver will be slick sided as well with out the forward assist.  For the ammo I cannot explain that.

ysgazelle
ysgazelle

Never knew there was a difference between them. I have fired both through my rifle without a problem. I prefer the AK and my M1A, but that is from being a Marine in Vietnam. I still dislike any variation of the M16. I know they have fixed all the problems, but I like weapons that will work even if dropped in mud.

rrockin90
rrockin90

I can personally account that I have shot thousands of military 5.56 rounds through a 223 and have not had one sign of any problems. In theory all sorts of things can happen. If you would actually look and see what the max chamber pressures are measured at the same point and testing basis. You would see that it is negligible at best. People should be more concerned about proper maintenance then with .223 or 5.56.

Jackhunter
Jackhunter

My Colt has .223 stamped on the receiver and 5.56 NATO stamped on the barrel. I think it is a 5.56. Is that correct?

LeviNSheraWoods
LeviNSheraWoods

@Jackhunter If the barrel is stamped .566 your rifle would fall under a multi caliber build, which is safe to shoot .223 and 5.56, alike. 

2013gs4lt
2013gs4lt

I have a manufacture who sells an AR15 in .223 but on the phone says it can fire 5.56 and the bbl has been tested. They say the chamber is a modified version so it can digest both types of without an issue. Should I take their word for it and shoot 5.56 even though its stamped .223?

Dawoogie
Dawoogie

@2013gs4lt 

After everything I've read online and people I've asked,say NO.
If the barrel was stamped 5.56, I'd say Yes.
I would ask to talk to someone else at the manufacture that is in a top position and have them email you something backing that they guarantee it will fire both, in writing.

Dawoogie
Dawoogie

I keep hearing & seeing armors, pawn shops and gun shops tell and post, that there isn't a caliber stamp on the Olympic Arms AR15 and the multi means it's .223 and 5.56. That's totally not correct. The multi Cal stamp on the lower where you put the magazine in means, it will receive different caliber ammo but NOTHING to do with the caliber of your barrel. All Olympic Arms barrels have been stamped with the caliber, period. Normally the stamp 5.56 or SS ect is on the top of the barrel, directly in front of the front sight. www.olypicarms.com doesn't say where on the barrel, which is annoying because it's so easy to not see caliber stamp. Pretty much every Olympic Arms barrel is stamped 5.56 not .223 since 2000, meaning that the barrel is designed for 5.56 and .223. I hope this helps someone because I kept overlooking the stamp and believed the shop I went to, the multi cal stamp.

casey
casey

So my husband kept saying that 22 ammo 223 ammo and 556 ammo are the same. I had someone ask about 22 ammo and my husband said that 223 and 556 are 22.  that didnt sound right so im trying to clear it up so i understand better. i have been researching the difference between these two and this was the most helpful information i have found yet. So what about the 22 ammo. Is that the same? can you us 223 and/or 556 in a 22 long rifle. Thank you to anyone who can explain

this a little better for me.

Jason in Oregon
Jason in Oregon

@casey @casey  A .223 rifle can shoot .223.  A 5.56 rifle can shoot 5.56 and .223.  A rifle that says .223/5.56 can shoot both .223 and 5.56.  A .22 rifle cannot shoot .223 or 5.56. You couldn't even fit a .223 round in the .22 rifle.  A .223 or 5.56 rifle cannot shoot .22 unless you have a special conversion kit, and even then it's not great - it's just not the intended use.  This image (http://bit.ly/1hA8MRw) will show you the clear difference between .22LR and .223.  


IsaacBarden
IsaacBarden

@casey What he means is that the diameter of the bullet is the same. If you shot a piece of paper with .22, .223, and 5.56, all three holes would look the same. 

neidlingermj
neidlingermj

@IsaacBarden @casey That is correct a 5.56MM round is .2189 inches in diameter. A .22LR is  between 0.223–0.2255 inches in diameter. 

Slowcala
Slowcala

Hi. I just bought my first AR. Bushmaster Carbon 15. The barrel is stamped .5.56 and the lower receiver is marked .223-5.56. In your opinion what would be the best round to fire through it? For safety more than accuracy. Just don't want to ruin the weapon or have a malfunction that could injure someone. Thanks

drmorris9
drmorris9

@Slowcala  You have a 5.56 chamber (the lower doesn't matter within a caliber family).  You may shoot 5.56 or .223 in that chamber without undue wear (it is the .223 chambers you have to be careful with).  The best accuracy will most likely be found with hotter 5.56 ammo, but assuming similar quality ammo, the difference will be negligible.

Slowcala
Slowcala

Thank you very much for your response. I do appreciate it.

csnetsurfer
csnetsurfer

The most important difference between .223 and 5.56 chambers is the length of the throat (or leade) for each chamber. I've heard that it is better to use 5.56 Nato in a .223/5.56 system, because of concentricity (keeping the chamber concentric). Grain effects the velocity the most, but leade distance might effect it ever so slightly (because of it being in the chamber length just slightly more (throat distance is more with better alignment). Better Ammo is important from what I heard also! 

drmorris9
drmorris9

Want to be even more confused? .223 Wylde (used by Rock River Arms and others) is in between these two chambers and can fire either round.

mmnetsurfer
mmnetsurfer

I have a DPMS upper that is stamped 5.56 on the barrel.    Will it handle a .223 round without any problem?    Should it be stamped with both .223 & 5.56? 

FateofDestinee
FateofDestinee

@mmnetsurfer  Seeing as .223 is lower pressure than 5.56, you should have no problem shooting .223 out of your 5.56 chambered rifle :]

csnetsurfer
csnetsurfer

I read about 5.56 being a little heavier than .223 and yes the throat being also the difference!  They also mentioned that running .223 in a 5.56 chamber can lead to concentric problems, because the .223 is smaller at the throat distance. The 5.56's have thicker metal jackets and create more higher pressures from what I read. My take is that it probably is better to use a higher grain if you plan to use the .223 in a 5.56 chamber, to get it past the threshold faster in the beginning. 

There are chambers that allow both .223 and 5.56 (Wylde chamber), but I am now figuring out that if it is chambered for 5.56, that your better off staying with the 5.56 and not using .223, unless your using a higher grain.

Just my take on how I believe things go!  


I have a DPMS AR-15 that takes both .223 and 5.56 by design and yes the 5.56 is more accurate and more powerful, but I would not use 5.56 unless I knew for sure that it is chambered for such! 

taino
taino

How the  "leade distance" on a 5.56 AR will affect the velocity or energy on .223 round? is like a double jump not?

drmorris9
drmorris9

@taino As the powder burns, the pressure increases, but as the volume increases (as the bullet travels down the barrel) the pressure decreases.  If the bullet meets the high resistance of the rifling sooner (shorter leade), it will initially travel down the barrel slower.  Since the powder is burning at a fixed rate, but the volume is increasing at a slower rate, this will cause higher pressure.  For this reason, the shorter the lead and the tighter the chamber (5.56 chambers are generally a little more generous) the higher the pressure spike.

It is harder to explain then to understand.  I hope that made sense.

WilliamStauffer
WilliamStauffer

im not very familiar with the 223 is the 5.56 better for long distance or the 223


SavageHenry
SavageHenry

I was looking at reman .223 and 5.56 penetration rounds.  the .223 and 5.56 of the same bullet weight were the same price and the numbers they listed put the .223 at just a bit faster and the 5.56 energy just a bit higher.  

 

In the instance of those reman rounds, I don't see much of a difference between the two because by the numbers, they should perform similarly.  

 

that's not to say that all rounds are loaded that similarly but I think when people see numbers being that close in certain instances, it adds to confusion.    

Muskrat
Muskrat

Thanks for the post Destinee. I've had so many people tell me that they are exactly the same, but I've seen the same info you posted. In fact, I think the most recent Gun Digest had an article about this that stated some 5.56 chambered rifles would not chamber a 5.56 plug gauge and needed to be reamed. Also they can ream out a .223 to be in between the .223 and 5.56 dim. so it would yield the best of both worlds they claim. Just info to think about.

Nate226
Nate226

how does it go? a 223 ar15 can shoot 223 but not 556, but a 556 ar15 can shoot both

peter3101
peter3101

ps We need to see a good video of Bruce and all his new accessories. 

peter3101
peter3101

I have a 5.56 M400, but shoot 223 at the range, I find it cheaper and it used to be easier to get. But I have the option of using 5.56 should I wish. 

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