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

Published on June 14th, 2016 | 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.


  • 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.

  • peter3101

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

    • 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. ;]

      • 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)

        • 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 ;]

  • Nate226

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

    • CK5150

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

    • FateofDestinee

      @Nate226 That about sums it up, yep. :]

  • 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.

    • FateofDestinee

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

  • 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.

    • FateofDestinee

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

      • 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.

  • Being able to have the option for either a 5.56 or .223 is always good. Just pray that more regs aren’t passed to stop sales.

  • 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 ???

  • WilliamStauffer

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

  • 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?

  • 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?

  • 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!

  • 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?

  • mmnetsurfer

    peter3101 
    Does the barrel say 5.56 and .223 or just the higher 5.56?

  • 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.

  • 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

    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.

  • 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.

  • 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.

  • 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 lead 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!

  • 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 lead 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!

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

  • 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.

  • 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

    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

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

  • 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.

  • 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

    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

    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

    IsaacBarden casey

  • roadtripbrent

    drmorris9 FateofDestinee SavageHenry .223 produces lower pressures.

  • 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. http://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.

  • 2013gs4lt

    I have a manufacture who sells an AR15  in .223 but on the phone says it can fire 5.56 and has been tested. They say the chamber is a modified on so it can digest both without an issue. Should I take their word for it and shoot 5.56 or just stay with .223 ammo?

  • 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.

  • roadtripbrent

    Is it .223 wylde? If so it will shoot both

  • 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

    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.

  • LeviNSheraWoods

    Dawoogie Yep, I have several Oly Arms barrels, all stamped 5.56.

  • KeithSwinney

    AlbDavidT SavageHenry 5.56 for the same projectile weight will be faster than a .223, as the 5.56 is loaded hotter. Higher weight projectile = lower speed in same caliber, but heaver also = more retained energy down range! 5.56 offers more options, you also have to consider the twist rate of your barrel, faster rate is better for light projectile, slower rate is better for heavy projectiles.

  • 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.

  • 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.

  • 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

    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.

  • 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.

  • 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?

  • mercus11

    KathyCat lady please tell me that you are kidding

  • TheCynabal

    Just a troll, ignore.

  • RobertSorbo

    KathyCat Try clamping them together then smackem with a big hammer

  • 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.

  • BenClifford

    You must be joking?

  • TxJack112

    KathyCat  Don’t give up you day job.. leave the comedy to the professionals…

  • TxJack112

    IsaacBarden casey  That is what I was gonna say is probably talking about diameter..  i.e .223-224

  • MissChris45

    KathyCat it’s easier to load 5 at a time through that hole if the butt of the weapon in on the ground and the barrel is braced against your shoulder.  Works like a charm! Give that a try.

  • DonavanMcCoy

    The problem is, you have to buy “AR15” ammo. Its hard to find but just keep asking.

  • dlcollins

    casey When reloading your own ammo your bullets are 22 /224 for a 223. This is probaly what your husband meant. He is correct.

  • ysgazelle

    KathyCat Come on, Hillary. Everyone knows you put the barrel end in your mouth and suck on it as you load the bullets. But don’t pull the trigger in this position and don’t slam the butt end on the ground. You may want to coat the barrel end with Old Log Cabin to give it a maple flavor while you load.

  • TaylorSmith3

    KathyCat  try looking down the barrel that might solve the issue.

  • Vinoman1953

    I too have the carbon 15 and have taken lots of chucks and two whitetail deer with it. I load .224 diameter polymer tip hornady Bullets. They are awesome performers and drop deer like my ’06 but admittedly, you need a well placed shot to drop ’em in their tracks. It’s a great lightweight rifle and investment in a .22 LR conversion is well worth it. It performs great in the carbon platform.

  • halfhitch05

    Keep trying g it’ll work some day! By the way how many kids do you have?

  • halfhitch05

    Shes gotta be a obama/Hillary fan!!!!

    • allwet

      Are you always a dick?

  • justbill 2

    Maybe you’d have better luck using 2 of the 23 rounds.

  • SlimShady69

    KathyCat You seems you have answered your own question and survived in tact. It seems the “hole” that you have in your AR-15 or whatever surely fits only one “bullet” at a time without most probably stretching or even ripping the “hole” wide open causing serious even irreparable damage to the “hole”. For your own safety Ms. KathyCat I would only put one (1) bullet in the “hole” at a time and that way by squeezing the trigger on your AR-15 OR whatever, you will get a big bang which will automatically remove the old used bullet from the “hole” and push another brand new clean and shiny bullet into the “hole” so as to safely get another big bang…

  • allwet

    ….chamber for .223 Wylde, easy enough……especially if you like the heavies.

  • Randy Knapp

    More importantly by going with 5,56 one can use any 5.56 or .223 brass includeing milsurp for reloading which is real important when using a progressive press as one you have you brass prepped meaning the primer pocket crimps gone you are good to go at cranking out ammunition.

  • allwet

    Same factors are involved w/ 7.62 N and .308 Win……

  • Larry Lowe

    Have 100 or so spent brass in .223 & 5.56. I want to reload them but I need to tell which round came out of which case. Anyone know how to tell them apart?

    • mark

      The head stamp on the case should tell you where it came from.

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