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.


36 comments
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.

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

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? 

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?

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. 

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. 

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.  


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.

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 :]

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.

drmorris9
drmorris9

@WilliamStauffer Technically the highest accuracy potential is .223 in a .223 chamber, however, most of us cannot do our part well enough to see the difference.  Advantages of 5.56 is being able to shoot a bigger variety of ammo safely, and in theory 5.56 is more tolerant to fouling (because the chamber is cut a bit larger) and thus is more reliable.  All these differences are very small.

AlbDavidT
AlbDavidT

@SavageHenry,

Can you check those listing numbers again? Maybe there were other details that accounted for the differences? For the same bullet weight higher velocity would make higher energy and lower velocity would make lower energy. I'm just going with physics here: energy = bullet weight x velocity squared. Maybe one did better over some distance ???

FateofDestinee
FateofDestinee

 @SavageHenry They are awfully similar... especially when considered that not every company (or home loader, for that matter) loads ammo exactly the same.

FateofDestinee
FateofDestinee

 @Muskrat There was plenty of stuff to dig through on the subject - which made for some very interesting, albeit time-consuming, research.

CK5150
CK5150

 @Nate226 yep.  most (but not all) AR's are chambered for 5.56 today.    

FateofDestinee
FateofDestinee

 @peter3101 True... once it stops snowing like crazy, I'll be hitting the rifle range a good deal more. I have a bunch of "toys" I have yet to cover that are better suited for the outdoor lanes. ;]

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

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

drmorris9
drmorris9

@FateofDestinee @SavageHenry  While manufacturers load to different specs, the only intrinsic differences between .223 and 5.56 ammo is the case wall thickness (a little thicker in 5.56), and the max pressure being a touch higher in 5.56, although most 5.56 ammo is not loaded to max.  The bigger difference is in the chambers.  .223 by spec (in the real world it varies between manufacturers) is a tighter chamber and shorter leade than 5.56 and as such the .223 will produce slightly higher pressures with the same ammo.

SavageHenry
SavageHenry

 @FateofDestinee  indeed.  also I have noticed that tula 55gr is labeled .223 but I have seen it advertized to use it in 5.56 chambered weapons because its a high pressure round.

 

it makes me wonder if its actually 5.56 they are selling as .223. they are head stamped .223.

 

there is just a lot out there and it seems convoluted.

ShawnOlson
ShawnOlson

@FateofDestinee @Nate226  So whatever is stamped on the upper on the actual rifle is what you shoud go by.  My AR15 only says .223 on it, so that is what I should shoot...  Great article.

peter3101
peter3101

 @FateofDestinee I hear you, but your pal Falia goes shooting in all weather conditions, but then again maybe she's made of tougher stuff.........just saying.   ;o)

peter3101
peter3101

Sometimes both, but if it say's 5.56 then you can shoot both calibers. If it says 223 then you can only shoot 223.

FateofDestinee
FateofDestinee

 @peter3101 Haha, I like Falia, so I'm not going to argue who is tougher lol.  I shoot in all weather conditions (check my vids), but I don't walk 60 miles in the snow while my car is in the shop ;] 

mmnetsurfer
mmnetsurfer

@peter3101   I just purchased a DPMS upper .223/5.56 and the instructions for breaking it in is to clean between every round for the first 10 rounds and then between every 10 rounds for several sets and then 25 rounds.    Is this normal?    I have never had a rifle or pistol that required that much effort in the initial firing.

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