5.56 vs .223: What’s the Difference? Does it Matter?

223 vs 556 ammo

Dan Z. for TTAG

What’s the difference between 5.56mm NATO and .223 Remington, anyhow? The rounds are supposed to be interchangeable…kinda, sorta, maybe…right?

The difference in the round itself: the NATO round is a little bit hotter. The case is the same size, but the powder charge, projectile and also the rifle specifications differ. As a result, make sure to check your AR-15 to see which it’s chambered for, as not all AR-15 rifles sold to civilians are the same.

NATO, you see, develops standardized loads so that any member nation has specifications for making the ammunition. As a result, a NATO round is a NATO round is a NATO round.

The standard loading is NATO SS109 (aka M855) which uses a 62-grain projectile. The powder charge for that round is on the hot side, which is loaded to chamber pressures around 62,400 psi in a rifle chambered for 5.56mm NATO.

In a rifle chambered for .223 Remington, the round produces chamber pressures upward of 70,000 psi, if going by SAAMI (the Sporting Arms and Ammunition Manufacturers Institute) standards.

By contrast, .223 Remington tends to produce lower chamber pressures between 52,000 and 55,000 psi, going by SAAMI specs. Therefore, 5.56mm NATO ammo isn’t safe for use in a rifle chambered for .223 Remington, but .223 is OK in 5.56. Thus, powder charge is the main difference between 5.56 vs .223 cartridges.

Wait. How can there be that much more chamber pressure when muzzle velocity for a 62gr pill – according to specs from Federal Ammunition for 5.56mm and .223 – is exactly the same?

5.56 vs .223


NATO specifies that any rifle chambered for 5.56mm have a longer leade than that employed for the .223 Remington round. The leade is the distance between the case mouth and the point at which the rifling begins in the barrel.

The .223 Remington chamber dimensions create a tighter seal on the projectile, and thus produces more pressure despite firing the same size projectile from the same case, given a slightly hotter powder charge, since more gas escapes with the larger leade.

The length and diameter of the leade — called the “freebore” — is longer and wider for the 5.56mm round, meaning there is a wider, longer free space the bullet travels in before it contacts the grooves in the barrel.

In addition to the higher pressure, NATO specs also call for any rifle made for use by NATO forces, including the M16, the M4 and other service rifles like the L85A2 of the UK or France’s FAMAS, have rifling with a 1:7 twist, or in other words 7 inches for a full 360 degrees of rifling rotation. This is so the NATO L110 tracer round (which has a longer projectile) can be fired from the same rifle as the standard ball round, as the optimal twist rate for the 62gr 5.56mm round is more like 1:9.

5.56 vs .223

Barrel rifling

Most civilian AR-15 pattern rifles have a twist rate of 1:9, which is actually something of a compromise. The slower twist rate enables the shooter to use different bullet weights, whereas a NATO-spec gun pretty much uses 62gr ball and 77gr tracer rounds only.

The civilian shooter could conceivably shoot a mix of 40 grain varmint rounds, 50 and 55 grain ball at the range, and even 62 grain ball when they’re feeling squirrely. Lighter bullets benefit from a slower twist rate (1:10 or even 1:12) so a twist rate of 1:8 or 1:9 makes it so you can get decent performance from anything.

So…5.56 vs .223. The former uses slightly more powder. Rifles chambered for it must adhere to certain specifications to suit it as it is a standardized military cartridge. The latter adheres to different specifications (such as a shorter leade), but has a much more diverse array of loadings from available from ammunition manufacturers. Case dimensions, however, are the same.

What this means in practical terms is that you won’t get the most out of actual 5.56 NATO ammo unless your rifle is made to NATO specifications such as the leade, twist rate, and can take somewhat higher chamber pressures. Thus, with its lower pressures, .223 can be safely used in a NATO-spec rifle in 5.56mm, but not the other way around.

Which brings us also to the .223 Wylde round. This isn’t actually a cartridge. Instead, it’s a set of specifications that enable a rifle to use both cartridges.

Put more accurately, it’s actually a .223 Wylde chamber. It was devised by one Bill Wylde, who came up with a solution allowing for the safe use of both bullets in the same gun while maintaining accuracy. This is accomplished by resizing the chamber for the same length of leade of 5.56mm NATO, but with the freebore diameter of .223 Remington. Either caliber headspaces correctly, preserving accuracy for both.

5.56 vs .223

Now…which one should you get? The NATO cartridge or .223? 5.56 vs. 223?

The answer is you should first consider what you want it for. A gun, any gun, is ultimately a tool, so therefore consider your task.

The .223 Remington chambering is the better all ’rounder. You can do a bunch of shooting at the range and in competition. You can load a bit heavier for hunting predators or varminting and since most .223 rifles have that slower twist rate, shorter leade and tighter freebore, the .223 will likely be more accurate.

That means it will be more precise at long range, though there are better rifle chamberings purely for long-range target work and varminting (.22-250 and .243 Winchester come to mind). There is also a better selection of ammunition for hunting other game — if you live in a jurisdiction that allows it — and for self-defense.

5.56mm NATO has fewer loadings commercially available and is also a dollar or two more expensive per box…but you get to say “mine uses military-spec ammo.” In terms of real-world capabilities of the round, that probably isn’t worth…well, basically anything. Is that worth much to you?

Let us know in the comments what YOU think about that.


This article was originally published in 2018.


  1. avatar enuf says:

    Mostly I have .223 Remington stacked up in the ammo closet, 55gr FMJ. Some 5.56 NATO, but not so much. All seems to go down range as desired, punches holes in paper, busts up clays, etc etc etc.

    I am aware of the differences but none of it seems to bother my plinking time any, so I pay it no mind.

  2. avatar Narcoossee says:

    Because of the reference to “civilians”, this implies that the AR-15 is, in fact a “military-grade” weapon: “As a result, make sure to check your AR-15 to see which it’s chambered for, as not all AR-15 rifles sold to civilians are the same.”

    1. avatar enuf says:

      Both of my AR-15’s claim 5.56 NATO chambers and M4 feed ramps. Neither is a weapon of war. So far, both as truly mean, cruel and heartless to clay’s and soda cans and steel plates and the odd Pro-Mag found laying out there where someone gave up on it.

    2. avatar Prndll says:

      The H3 Hummer is a civilian version of the original Hummer (H1) that was intended as a military vehicle.

      There are all kinds of things like this.

      1. avatar GS650G says:

        Except the H1 is a real off road vehicle and the H2 and H3 were chevy trucks with a different body. Take a look under a H1 and you’ll see the difference.

        1. avatar I Haz A Question says:

          The H3 comes with a suburban soccer mom that drives 5 mph slower than the speed limit and doesn’t know what the turn signal is for.

        2. avatar Prndll says:

          I remember seeing the H1 for the first time at a car show. If it were an option, I would have bought it right there. It was the only kind of Hummer that I ever thought was worth having. Then the H3 came out and I fealt such a let down. It’s a similar kinda feeling when I saw what the Ruger Mark 4 pistol got changed into. After mastering the MarkIII, it just seemed like a waist of money.

        3. avatar Geoff "Ammo. LOTS of ammo..." PR says:

          “The H3 comes with a suburban soccer mom that drives 5 mph slower than the speed limit and doesn’t know what the turn signal is for.”

          AS long as she wasn’t frigid, I might be able to deal with that.

          With a pony-tail and yoga pants, sold!

          (Misogyny-R-Us… 😉 )

      2. avatar Tommy357 says:

        I have a civilian version of a military grade satellite guidance system – it’s called an iPhone with iMaps. In the wrong hands it could guide an ICBM to within an inch of any target on the planet.

        Fortunately, I am a legal guidance-system owner.

        1. avatar Dave in PTC says:

          Tommy, you seem like a dangerous man.
          I’m gonna keep an eye on you.

        2. avatar Geoff "Ammo. LOTS of ammo..." PR says:

          “In the wrong hands it could guide an ICBM to within an inch of any target on the planet.”

          Actually, an ICBM is a hard no-go. ‘Baked-in’ the silicon with the publicly-available chipset it will not function over a certain velocity. So, with an inbound 17,000 MPH missile, it just sits there going ‘Derp.’…

        3. avatar David says:

          Cruise missile it is then. Easier to build and test without drawing any undue attention anyways.

  3. avatar Biff says:

    I don’t know how you can conclude .223 is the best option. If you get a .223 Wylde or a 5.56 you can shoot any available ammo from 40 to 77 grain.

    The only reason to get a dedicated .223 is in a bolt gun or specialized AR15 to shoot light 40-55 grain bullets. If you want to hunt varmints it might be a good choice.

    For an AR15 a .223 Wylde in 1:8 twist will probably be the most accurate with commonly available ammunition.

    A 5.56 NATO chamber with a 1:7 twist is also a good choice since most milspec rifles commonly come this way. For a mass produced 16” carbine there really isn’t much accuracy difference vs the .223 Wylde unless you pony up for a premium barrel.

    1. avatar J. Smith says:

      Exactly Biff. In my AR’s I use 1-8 Wylde twist and chamber, no worries and accuracy is good, sometimes even great. Dedicated bolt actions or precision guns, go with .223. . I have a 26″ hb with 1-12 twist, one holes 40g v-max all day and gets 4,000 fps.

    2. avatar Jerms says:

      Honest question…what is .223 wylde? Does it just let you shoot 5.56 and .223? If so, why is it a different name? Ive glanced online but its still not clear to me

      1. avatar Biff says:

        .223 Wylde isn’t a cartridge, it refers to how the chamber is cut. It was designed to be able to shoot both standard 5.56 NATO military ammunition and heavy bullet (75-77 grain) match rounds more accurately than a standard 5.56 NATO chamber. Bill Wylde did this by changing the leade, or the chamber throat (the transition from the chamber to the rifling) so it was tighter than a NATO chamber, but still had enough room to safely accommodate longer bullets.

        If you are buying a premium barrel it is a good option. I’d be kind of wary buying a bargain bin rifle with a Wylde chamber though. I’d rather have something like a BCM with a NATO barrel than a cheap rifle with a Wylde barrel.

        1. avatar Jerms says:

          So it’s like a 5.56 barrel/chamber but optimized performance of heavier 5.56 bullets if I understand correctly

      2. avatar Someone says:

        It is explained in the article.
        Pay no attention to the headspace note. While it’s not wrong, both .223 and 5.56 headspace on the case shoulder and it has nothing to do with differences in lead.

    3. avatar raz-0 says:

      This article mashes enough things together into assumptions that I question if those assumptions are based on knowledge and experience or ignorance.

      Specifically comparing the cartridge pressures. Yes, nato pressure is roughly 62,400. But that pressure is gotten by a different method (EPVAT) than SAAMI uses. A saami 55,000 psi is not an epvat 55,000psi. The military has another method of measuring pressure called SCATP whihc is much more analogous to saami’s method. And the spec for 5.56 using that method is 55,140 psi. Which might as well be the same as the saami pressure specs.

      So where did they pull the 70,000 psi number form and which method does it use? Because as you can see it matters a lot where you take the pressure reading. It’s why CIP doesn’t match SAAMI doesn’t match EPVAT. 70,000 EPVAT vs 62,366 is less of a deal than 70,000 SAAMI.

      Then of course there’s the fact that chamber reamers are all over the place. You have some .223 ones that are more generous than some 5.56 ones. So what is stamped on the barrel doesn’t necessarily mean much.

      Then there is brass. 5.56 technically holds 28.5 grains of water, and .223 28.8 grains. Does it matter? only if you are loading to the bleeding edge and not sneaking up on it form the safe side. Even then, I have seen .223 sold with new lake city brass from big names, so…

      From a consumer standpoint, I just buy 1:8 .223 wylde barrels and call it done and just don’t push my loads to the bleeding edge.

      Also the articles talk like you’ll blow your gun up and this is something to care about. the ammo will warn you it’s a bad fit by popping primers and or splitting case necks. If your doing that, stop with that ammo and rifle combo, regardless of mix and matching. It’s really the only warning you get that means anything given the variation in chamber reamers.

  4. avatar Nate in CA says:

    In my eyes it’s still just a poodle popper – I respect it from an logistics/effectiveness perspective, but it’s not enjoyable to shoot. Unless you’re building a TEOWAWKI gun, stick with .223 (or better yet, 7.62x39mm).

    1. avatar enuf says:

      According to recent news, Orlando Bloom (the actor) is missing a poodle.

      Please hold of on any “popping” of that sort, there’s a $5K reward being offered.

    2. avatar Username says:

      You look like a poodle to me.

    3. avatar TJW says:

      Poodle is French for puddle

    4. avatar Someone says:

      What is not enjoyable about shooting the .223/5.56? Is it it’s decent accuracy? Low recoil? Light guns?
      Almost all people I took to the range for their first time say they enjoyed my .223 Wylde AR15 most. My 11 years old son loves to shoot it. I enjoy it just fine too.

    5. avatar adverse6 says:

      The 5.56 NATO is the Border Collie of military rounds, it’s main job is to herd the opposition into a kill zone for the heavy stuff.

      1. avatar edward kenway says:

        Which is why the Army is going to the 6.8mm round.
        Still, as a ballistics nut I can’t see why they didn’t go with the 6.5×42 MPC which is a shortened 45mm brass case. It has better performance without being a barrel burner and still fits well with ARs … but the Army wants a new 6.8mm replacement despite the years of 6.5mm performance.

  5. avatar Dude says:

    “5.56mm NATO has fewer loadings commercially available and is also a dollar or two more expensive per box”

    The last time I bought it at Wal-Mart, it was the exact same price for the same brand and grain. The NATO was loaded slightly hotter.

  6. avatar Sam I Am says:

    These type postings are always welcomed. Can’t understand why/how I missed this in 2018.

    1. avatar I Haz A Question says:

      Me either. Must’ve missed it entirely.

      Me? For these two cartridges, I take the simplest path. My AR for this chambering is spec’d for 5.56, so I have 5.56 premium ammo for TEOTWAWKI, but practice my drills mostly with cheaper .223. That’s as “operator” as I get with it.

    2. avatar Cletus says:

      You would think they would at least edit out the mistakes before republishing the article.

      1. avatar Sam I Am says:

        “You would think they would at least edit out the mistakes before republishing the article.”

        Some of us don’t have the experience to identify the mistakes. I just have to take rifle articles at face values until the comment section provided clarification.

  7. avatar Frank says:

    Damn, I don’t know. As long as 5.56 ammo is available, I don’t care if it is NATO standard or not, except maybe for the desire to use that specific ammunition such as an end of society apocalypse where I might need to scrounge or trade or beg for ammo from military sources.

    I am one who believes in using what works best for you. Although for example, .38 long is easier to find than .38 Super, but if you can handle and shoot a firearm that uses it, then I say buy it. I own an old Mauser and I love it, but ammo is hard to find now, but not impossible, so for occasional use it’s acceptable. Then again, maybe one day those calibers will make a comeback like anything that people show an interest in.

  8. avatar Rad Man says:

    Does it matter? No, neither caliber matters. Now, 6.5 Grendel and 762×39 matter!

  9. avatar Prndll says:

    These kinds of articles are great. It was the original reason I started coming here in the first place. I think more people would benifit from this type of thing.

  10. avatar Mark N. says:

    I built my rifle with a 1:8 Wylde chambered barrel so I wouldn’t have to worry about it.

    1. avatar Geoff "Ammo. LOTS of ammo..." PR says:

      Smart move.

      Now, can a .223 or 5.56 barrel be re-chambered into a Wylde?

      (My old Mini-14 chambered for .223 ate 5.56 with nary a hiccup. Then again, that gun was more accurate than I was able to shoot it, anyways…)

      1. avatar Mike V says:

        I think the mini is 5.56, even though it is marked .223
        Had to look into it a few years ago and that’s what I discovered.

        1. avatar Huntmaster says:

          Some of them are, some of them aren’t. You need to know if yours is.

      2. avatar Mike V says:

        Wait, did you just compliment the accuracy of your mini?

        1. avatar Geoff "Ammo. LOTS of ammo..." PR says:

          “Wait, did you just compliment the accuracy of your mini?”

          No, it was a ‘mea culpa’ of how bad I suck as a rifleman… 😉

        2. avatar edward kenway says:

          That’s funny, but true.
          I bought a Mini 223 folder years ago and gave it to my dad. The higher ammo capacity seems to give him confidence … that, and he’s older and doesn’t want to deal with the recoil of magnum revolvers.

      3. avatar Ing says:

        Based on the article’s limited info, I’m guessing a .223 chamber could be Wylded (increasing the leade), but 5.56 probably can’t, because the extra space already in the chamber can’t be undone.

        I went for a 5.56 NATO chambering with 1:8 twist when I snagged my AR because the uppers with Wylde chambers were more expensive and I wanted a rifle that would shoot *all* the available ammo with reasonable accuracy.

        I can pick up whatever’s cheapest for target practice without regard to bullet weight (it’s almost always 55gr .223 or 62gr 5.56 Tula crap), and I keep a couple of mags loaded with Frontier open-tip match in case I need to repel invaders.

        Basically, I’m following the AR ownership manual for cheapskates.

      4. avatar Ironhead says:

        I do not believe the chamber can be converted to a wylde.

        1. avatar Geoff "Ammo. LOTS of ammo..." PR says:

          At one time in the past, Ruger offered a Wylde chambered Mini-14…

  11. avatar former water walker says:

    My defense AR magazines are loaded with M855 green tip,Federal M193 ammo and whatever quality 223 for the remainder(anyone use 223 Frontier soft point for defense?) At the range whatever brass 223almost I have. Smith & Wesson Sport 16″ barrel 1in 9 twist…almost all the ammo bought cheap.

  12. avatar Matt says:

    They skipped over the mil. case wall being thicker than .223

    1. avatar Curtis in Illinois says:

      And since the .556 case has less capacity because of the thicker wall, this is going to be a potential consideration if you reload.

      1. avatar Jim from LI says:

        The .223 case holds .02 ml less water than a 5.56; does this really affect the pressure generated with the same powder load, or does it only increase the case durability with NATO-spec loads?

    2. avatar Biff says:

      Mil cases are usually heavier in 7.62×51 vs .308.

      When it comes to 5.56 vs .223 it isn’t necessarily true. The heaviest cases I’ve seen have all been .223

  13. avatar GS650G says:

    My boxes say .308 or 7.62 x 51 mm so I can’t possibly have an opinion on the varmint rounds.

    1. avatar EpsteinDidNOTKillHimself says:

      I reload, have not bought factory ammo in nearly 2 decades, so, it is possible to reload 7.62×51 for varmint rounds.

      To the article, if I were so inclined to have a AR15, likely I would have a 5.56NATO and call it good.
      Having to concern myself with the what is it caliber is an additional worry I would rather not have.
      Per all the crazy that we are currently seeing in the US let alone the world, I think it only prudent to opt for the lest amount of arse pain or worry about if that round in your chamber is gonna result in a catastrophic failure or not.

      1. avatar GS650G says:

        223 is based on. 222, a varmint round. I shoot rounds that deliver lots of energy.

        1. avatar Swoon says:

          Youre so cool 😍

  14. avatar mrpski says:

    After shooting a mil spec AR 15 for 50 years I finally bought another one, 5.56 with the Wylde chamber 1.8 and it is more accurate than the old one, course the old one had maybe 5000 rounds through it and Lord knows how many before I got it. Whether it is 50 or 500 yards a pie plate is good enough for me I never considered a bulls-eye invasion so I am good.

  15. avatar Andy G says:

    Fun Fact: In the UK (and probably the rest of Europe/EU) rifles are proof tested to CIP standard. .223 is a SAAMI spec cartridge and has no CIP spec so the proof houses in the UK test to the nearest CIP cartridge which is 5.56 NATO. So any rifles sold in the UK as .223 have been proof tested as 5.56 NATO.

    1. avatar GS650G says:

      All three of them IOW.

  16. avatar Darkman says:

    As I understand it. .223 dedicated rifles are not designed to handle the chamber pressure of the 5.56 round. I shoot both in my Bushy with equal accuracy out to 100 meters. Anything that needs to be dead farther out gets the .308.

  17. avatar Auggie says:

    Have any of you heard of a KABOOM happening because someone put 5.56 ammo in a barrel marked .223? I haven’t. If I were a barrel manufacturer, I would make sure that even barrels marked .223 would handle 5.56 ammo. Being a litigious society and all.

    1. avatar Prndll says:

      Your in luck. That’s exactly what they do now. Just to make sure there is no confusion though they add the word “Wylde” to the stamping.

      1. avatar Montana Actual says:

        lol. Almost like you read the entire article…

    2. avatar RGP says:

      Gunmakers would have been sued into oblivion since the 1960’s if you could blow up their products by firing 5.56 in a gun marked .223.

    3. avatar Andrew says:

      Worst I’ve seen in a bolt action Remington chambered in .223 was that you couldn’t cycle the bolt after a single round of 5.56 until the chamber had completely cooled. Couldn’t get the bolt open with a Hammer and a Wooden block. That casing expanded and wedged itself in the chamber.

    4. avatar Andrew says:

      Worst I’ve seen in a bolt action Remington chambered in .223 was that you couldn’t cycle the bolt after a single round of 5.56 until the chamber had completely cooled. Couldn’t get the bolt open with a Hammer and a Wooden block. That casing expanded and wedged itself in the chamber. So yes, it does matter if your rifle is chambered for .223

  18. avatar Montana Actual says:

    In 2020 if you are not using a .223 wylde build, you are way behind and probably low on ammo 😉

  19. avatar 5spot says:

    Correction maybe??
    Shouldn’t it read 5.56 has pressures of 70k psi, not .223 Rem?

  20. avatar Rob Driggs says:

    I reload both 223 and 5.56 cases with 27 grains of Hogdon CFE 223 powder for a 55 grain bullet and they both shoot well from my Remington 700 bolt action and my AR 15s . The twist rates vary from 1 in 10 to 1in 7 .

    1. avatar Southern Cross says:

      And I thought my 55g load of Winchester .223 cases, Winchester small rifle primers, and 25.5g of AR2206H was on the hot side. I’m amazed 27g of powder will fit into a .223 case and seat a projectile to SAAMI length.

      1. avatar Someone says:

        Hogdon CFE 223 is very fine grained. It may fill the same volume with little more weight compared to extruded powder. Hodgdon data shows max load of 27.8 gr at 51,300 psi.

  21. avatar Mike Carbine says:

    Funny thing is that standard issue Brit 5.56mm would not cycle in our US M-4s till the buffer & extractor springs were swapped with stronger ones. But it’s all the same NATO standard right…not really.

  22. avatar Craig Shue says:

    With all that has been said there is one certainty. Any time a primer is ignited and charge sends a projectile down a barrel a liberal sheds a tear, so FIRE AT WILL.

    1. avatar Southern Cross says:

      Who is Will?

      1. avatar Captain Obvious says:

        A liberal.

  23. avatar Wally1 says:

    5.56 or .223, none of this matters because there will never be any peace in the world until you start using your turn signal.

  24. avatar BradB says:

    A few years ago I stumbled on a super deal so bought RRA AR4s for all the kids (grown adults) and the brother & sister-in-law. These were all chambered in 5.56. I had a lot of .223 55 grain on hand so we spent the first range day burning some of that up. We learned the hard way that the .223 would not reliably cycle the rifles. Maybe now, after a few thousand rounds through most of them they would do better, but the gas system appears to be tuned to the chambered round, so be aware of that when running .223 through a 5.56 chamber.

    1. avatar Andrew says:

      Can’t you adjust the gas system on those rifles?

      1. avatar BradB says:

        It takes an adjustable gas block. I put one on my .308. These all had the A2 front sight (gas block as part of the sight) so there is a little more to it than just unbolting one part and popping on another. (Not too difficult – go get YouTube certified. It’s do-able.)

        Perhaps you could overcome it by playing with the buffer and/or spring but I am not enough of an AR expert to reliably comment on that. Likely someone will be along shortly though. Stay tuned.

  25. avatar Markie says:

    If I were t have but one .223 barrel, it would be Wilde chambered. I can’t see a reason not to.

    1. avatar Chris. says:

      Yes – this is of course the correct answer.

  26. avatar Mark Kelly's Diapered Drooling Ventriloquist's Dummy says:

    Why even bother with all this BS, just shoot 7.62 x 39 out of SKSs and AKs and be done with it.

  27. avatar Chris. says:

    So, next question – How do you pronounce Wylde?

    I’ve heard both “Wild” & “Will-dee”?

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