The differences between .223 Remington and 5.56mm NATO have been hashed out many times on the internet. Unfortunately, many of the “facts” that are often thrown around are simply what someone has heard from someone else, leading to a lot of misinformation being accepted as gospel.

In order to create this article, I temporarily set aside all of my previous knowledge and opinions while several months’ worth of new research and experimentation on the topic was undertaken. In addition, extensive discussions with gunsmiths, ballisticians, and laboratory technicians were conducted.

My findings, and the opinions of many experts in the industry who deal with the topic every day, were not exactly what some might expect. In fact, many of them had already discovered what I am reporting, although my research was conducted independently.

This article is not a recitation of previously existing information. It is quite long and complicated; if you don’t have the time or inclination to read everything, a (bold ) summary may be found at the end of most sections. However, I attempted to write it in a manner which should be easily understood by all – so if you want to read the whole thing, you will come away with a more complete understanding.

Basic Knowledge

You should never fire 5.56 ammo in a .223 chamber…right? What would happen if you did?

Prvi Partizan M193 5.56x45mm Ammo Image

If you’re unfamiliar with the differences between .223 and 5.56, you should understand the following basic facts:

  • The exterior (physical) dimensions of .223 and 5.56 ammunition are effectively identical.
  • 5.56 ammunition may be loaded to higher pressures than .223 ammunition.
  • 5.56mm chambers are dimensionally larger in certain critical areas than .223 chambers.
  • Given the same ammunition, 5.56 chambers will have lower pressures than .223 chambers.

How are .223 and 5.56 Ammunition Different?

The development of what has become .223 and 5.56 began many, many years ago. You can find an excellent history of this development on The Gun Zone. There is little point in restating what has already been written well.

However, it’s important to note that as military development of the 5.56mm cartridge has required higher velocities (via higher pressures), civilian development of .223 has essentially remained frozen since December 1962, when Remington submitted the cartridge for standardization by SAAMI. You’ll note that I didn’t say 5.56 was standardized by SAAMI, and that’s because it hasn’t been. Only the dimensions and pressures of .223 Remington have been standardized.

Can you tell which of these rounds are .223 and which are 5.56? Because .223 Rem and 5.56 NATO share the same external dimensions, it can be hard to tell the difference.

Because SAAMI specifies that pressures must be measured one way and the military specifies that they must be measured a different way, a direct comparison of pressure results from one lot of 5.56 ammo (measured the US Military way) with another lot of .223 ammo (measure the SAAMI way) is not possible. It’s required to test both with the same methods, instrumentation, and chamber to see any real differences.

Theoretically, any manufacturer could make ammunition which exceeded the maximum pressure specified by SAAMI for the .223 cartridge and call it 5.56. That pressure could be exceeded by 1% or 10% – it really wouldn’t matter. It’s the functional equivalent of “+P+” ammunition – there are no official guidelines for it which ammunition manufacturers have agreed to follow, as is the case with SAAMI. You could almost consider it to be the world’s most popular wildcat cartridge, as far as SAAMI standards are concerned.

Despite this lack of SAAMI standardization, most of the 5.56 ammunition on the market is manufactured by companies that produce 5.56 for various militaries; the 5.56 they sell to civilians is essentially identical, and thus follows the requirements and maximum pressures set forth by those military clients. As you can see from this short excerpt from a 27-page specification for US Military ammunition, military requirements are very exacting.

Military requirements for ammunition are quite stringent.

But those military clients are purchasing ammunition for military rifles, which brings me to the next difference between the two: chamber dimensions.

Summary: While .223 Remington chamber dimensions and maximum pressures have been standardized by SAAMI, 5.56mm NATO dimensions and pressures have not. Partially because of this, ammunition pressures are measured differently between the two, and cannot be easily compared. Still, it is generally agreed upon that 5.56mm ammunition may be loaded to higher pressures.

.223 Chambers, 5.56mm Chambers, Everything In Between – And Beyond

If you’ve read about this topic before, you’ve been told not to fire 5.56 in a .223 chamber. The possible results from this, you may have been told, can be catastrophic – the destruction of your firearm, and, at the same time, you might be injured or killed. It’s scary, but not quite true.

.223 Remington ammunition is pressure tested in what is called a “SAAMI Minimum Spec” chamber – that is, a “worst case scenario” chamber in this regard, made to the smallest dimensions, which would result in the highest pressures with any given ammunition. In reality, the likelihood of encountering such a chamber outside a testing lab is incredibly small. Many .223 Remington chambers will see maximum chamber pressures which are several thousand pounds per square inch (PSI) lower than those seen in SAAMI test barrels.

These SAAMI specifications for .223 Remington chamber dimensions allow for a range of minor differences between manufacturers.

At the other end of the spectrum are 5.56mm NATO chambers, which will exhibit lower pressures than .223 Remington chambers with the same ammo. Sometimes, even 5.56mm dimensions are exceeded. These “5.56mm Plus” chambers are sometimes reamed (machined) intentionally to provide the most insurance against excess pressures, but other times they’re just the result of careless machinists.

In between are chambers designed to balance pressure and accuracy, for the long freebore and throat dimensions of 5.56 NATO chambers are often blamed for reduced accuracy in comparison to .223 Remington chambers. These include .223 Wylde and 5.56mm Noveske Match Mod 0. Even among these, there are differences in reamers – one company’s idea of .223 Rem is not the same as the next. Take a look at this comparison chart and you’ll see a dizzying array of differences.

 

This chart shows a wide variety of differences between each reamer company’s idea of .223 or 5.56 chambers – and it doesn’t show all of the variations on the market (data courtesy of AR15Barrels.com).

What all of these chambers have in common (with the exception of the Noveske chamber, which is produced by only one shop) is that they are reamed by a wide variety of machine shops and personnel who may or may not be experienced, skilled, or caring. When you buy, for example, a .223 Remington rifle, you’re probably not getting a chamber that’s identical to the others on the shelf.

The Maltese cross is used by Noveske Rifleworks to identify the proprietary 5.56mm chamber reamed in their barrels.

You’re getting one that is, if it was manufactured by a reputable company, somewhere within the range of acceptable tolerances for a .223 Remington chamber. If it was made by a company with more of an emphasis on cost savings than exact machining, it could be a minimum spec .223 chamber, or something that is closer to 5.56, or anywhere in between. Even between chambers reamed by a reputable company, differences exist, as you will see.

In addition, the pressures of different types of ammunition can vary wildly – this is, like many things I mention in this article, a topic for another day, but I saw pressures between 45,000 and 63,500psi while conducting this testing. The .223 Rem and 5.56 NATO max pressures of 55,000 and 62,000psi, respectively, do not mean that you will actually get ammunition loaded at that pressure. .223 tends to be loaded lighter and 5.56 tends to be loaded hotter – but there are exceptions to these general rules.

Summary: Instead of there being two or three or four possible chambers (.223 Rem, .223 Wylde, 5.56mm Noveske, 5.56mm NATO) and two possible pressure levels of ammunition (.223 Rem and 5.56mm NATO), there are a nearly infinite number of points between the extremes. This can result in differing pressures with the same ammunition. It’s possible to ensure that you have something closer to the chamber you want to buy via purchasing a high quality rifle (or upper receiver assembly, or barrel) from a known source.

How I Tested Maximum Average Pressures

In order to test how 5.56 and .223 ammunition behaved in different chambers, I used a .223 Remington bolt action rifle and two 5.56mm AR-15 rifles, strain gauges, and pressure monitoring equipment. All gauges were attached at the midpoint of the case, which is where SAAMI tests pressures; military/NATO pressures are measured at the case mouth. All three barrels were 20″ in length. The Weatherby Vanguard Compact .223 Remington barrel had a twist rate of 1/12 and was not chrome lined; the FN 5.56 barrels were 1/7 twist and chrome lined.

Federal XM855 ammunition and FN 20″ 5.56mm AR platform rifles were some of the ammunition and firearms tested.

Because I’ve just finished explaining how there can be a wide variety of dimensions for a given chamber, it should be fairly obvious that a small sample size of chambers for pressure testing cannot possibly represent every possible combination on the market. However, I felt that it was better to test a large amount of ammunition in a few rifles than only a few rounds in a large amount of rifles (the results were still quite educational).

Most of the ammunition tested was manufactured by Federal – AE223 and XM855. These are representative of the more popular types of ammunition on the market – 55 grain FMJBT .223 and 62gr steel penetrator FMJ SS109/M855, which is currently used by the military, although it has begun to be supplanted by other types of 5.56 ammunition. Here’s a sample pressure graph of Federal XM855 in a 5.56mm chamber, with velocities and pressures that match Federal’s specifications for the ammunition.

As pressure curves for production ammo go, these ten shots of Federal 5.56 ammo in an FNH-USA 5.56MM chamber were relatively consistent.

 

The observed chamber pressure for Federal XM855 5.56mm ammunition in a .223 Rem chamber exceeded .223 maximum pressures, but not by a massive amount. The ninth shot (the red line separate from the others) was an underpowered cartridge which exhibited significantly lower velocity and pressure than the other rounds, so it was excluded from the average velocity and pressure numbers for this chamber, because it would unnecessarily skew them too low.

 

Federal AE223 was loaded consistently and offered significantly lower pressures in 5.56mm chambers, while still cycling the actions of mil-spec AR platform weapons.

 

The secondary pressure spikes seen in this graph may be discussed in a future article on LuckyGunner Labs.

 

The secondary pressure spikes and ignition delays seen in this graph may be discussed in a future article on LuckyGunner Labs.

Because of their consistency, and because .223 Rem pressures should be at least more similar from barrel to barrel than 5.56 pressures, Hornady .223 Remington ammunition was used as a “calibration load” for the pressure monitoring equipment. In essence, it is required to use a load of known pressure to calibrate the equipment and provide a useful comparison with any other type of ammunition or chamber.

This method provides a much closer and more useful comparison than the differences between SAAMI and NATO testing methods.

How the strain gauge comparison can be useful is to see what increases in pressure result from the use of different types of ammunition in each chamber compared to that calibration load. If we eliminate other variables and see a massive increase in chamber pressure from .223 to 5.56 in one barrel that we do not see elsewhere, we know that the dimensions of that chamber are different enough to cause that increase.

Strain gauges and a PressureTrace II system were used to collect the data shown in this article.

In order to ensure that I was getting the most accurate maximum average pressures possible, I contacted the manufacturers of a number of different types of ammunition with the results I had found. Of the manufacturers that responded, none informed me that my maximum pressure results were inaccurate (although they were understandably reluctant to disclose their proprietary data).

Summary: I tested .223 and 5.56 ammunition in one .223 and two 5.56 rifles with pressure monitoring equipment. While the results are not perfect and cannot provide absolutely equal comparisons between barrels due to chamber dimension differences, my calibration/baseline maximum average pressure results were confirmed to be accurate by several different ammunition manufacturers.

What Happens When You Fire 5.56 Ammo in a .223 Chamber?

I know most people are interested in this part – and yes, I really did fire 5.56 in a .223 chamber. I had a friend at the range with me at the time, and he stayed a good ways back when I did so. I was not concerned about what would happen, and as I expected, the results were not spectacular.

However, I was surprised about the results I saw. There was no dangerous spike in pressure from firing 5.56mm ammo in a .223 chamber. While pressures were elevated in comparison to one of the 5.56mm barrels, they were slightly below the other 5.56mm barrel.

This unexpected difference was also borne out by chronograph measurements, which showed that the Weatherby Vanguard Compact bolt action rifle fired the XM855 ammunition (all of which was from the same lot) at a velocity which was higher than the lower pressure 5.56 barrel, but lower than the higher pressure 5.56 barrel. It’s true that the .223 barrel showed about 5% more pressure for less than 1% more velocity than the lower-pressure/lower-velocity 5.56 barrel, but the difference was not astoundingly large, as some might have expected.

In fact, the higher pressure 5.56 barrel – which was in the same condition as and made on the same production line by the same manufacturer as the lower pressure 5.56 barrel – was putting out XM855 at an average velocity within spitting distance of 3200 feet per second. As my gunsmith friend has told me several times, velocity is a sign of pressure, and this second 5.56 barrel showed both increased velocity and increased pressure compared to the other two.

Does this mean that everyone should start firing 5.56 in their .223 chambers? No.

I must now go back to the “previous knowledge and experience” I mentioned that I had, for the most part, discarded when conducting this experiment. I have owned approximately sixty AR-15 barrels, with a fairly even distribution of .223 and 5.56 chambers, plus Noveske and .223 Wylde chambers. I have also owned numerous bolt action rifles chambered in .223 Remington. I have fired .223 and 5.56 ammunition in most of these barrels and rifles.

Although my results are still anecdotal, I do not recall seeing anything worse than popped primers from firing 5.56 in a .223 chamber (or 5.56 in a poorly machined “5.56 chamber” that isn’t really a 5.56 chamber). It’s important to note that most of the .223 chambers I’ve fired 5.56 in didn’t show any signs of excess pressure, although I didn’t chronograph each and every one.

If a popped primer lands inside a fire control group (where the red arrow is pointing), it could cause the weapon to stop functioning.

 

Popped primers are definitely a sign of excess pressure or an abnormal pressure curve, and should not be ignored. They can become wedged in some of the more important bits of an automatic rifle, causing it to stop functioning, and while this could be annoying at the range, it could also be fatal in a self-defense situation.

Summary: Velocities and pressures for 5.56 ammunition in a .223 barrel were not significantly higher than the same ammunition in a 5.56 barrel; in fact, they were in between the two 5.56 barrels. This doesn’t mean that your barrel will have the same results, and you should always be aware of pressure signs when holding metal objects containing 50-60,000psi of pressure only a few inches away from your face.

Shouldn’t Your Rifle Have Blown Up?

My greatest concern while researching, experimenting for, and writing this article was whether or not I was putting out accurate information. In order to double check my results, I consulted with over half a dozen industry professionals, all of whom have far more experience in this area than I do. They work for highly respected laboratories, companies, and organizations.

This AR-15 upper receiver was destroyed due to extreme overpressure, but this was not the result of firing 5.56 in a .223 chamber.

While I do not wish to put words in their mouths, none expressed great concern that I would have a rifle blow up in my face during the course of my experiments. In fact, most said that the actual differences are, in effect, “not a big deal.”

That said, one noted gunsmith told me about a test he had heard of, conducted by an ammo manufacturer, in which 5.56 in a .223 barrel exhibited pressures of 77,000 PSI. I have no doubt that this is true and do not wish to cast doubt on what he said – however, I am also certain that that ammo manufacturer was performing the test with a SAAMI test barrel, which, as I said before, is much “tighter” than any barrel which is likely to be encountered in the real world.

Barnes Bullets tested XM855 and AE223 in their test barrels for us, using the conformal transducer method at the midpoint of the case – the SAAMI method. Their results were slightly different from ours, which can be expected due to the different barrels and the different testing methods, as well as different lots of ammunition, but overall the results were quite similar. Note that the .223 velocities are higher because the barrel was 4″ longer.

Barnes Bullets, manufacturers of high-end hunting and defensive ammo, tested 5.56 and .223 in their 5.56 and .223 test barrels. Their results did not show excessive pressures either.

 

Velocities for .223 are higher than 5.56 because the .223 test barrel was four inches longer.

Encountering an undersized chamber in the real world is likely, especially if it was manufactured cheaply and with little quality control procedures. Among some companies, there is a definite “race to the bottom” which can result in subpar and unsatisfactory components. I now spend just a little more money on my guns and equipment, and get a lot more quality. If you would like to check your 5.56 chamber to see if it really is 5.56, order a .223/5.56? Gage from Michiguns.

Summary: The majority of the experts I consulted over the course of my research did not feel that there was a major difference between .223 and 5.56 chambers in terms of pressure.

Don’t Hammer Forged Barrels Have Perfect Chambers?

Without going in to too much detail about manufacturing processes which are not relevant to this article, one of the selling points that is often mentioned for hammer forged barrels is that the chambers are forged along with the rifling, meaning that they are properly sized and there are no worries about the quality of whoever reamed the chamber. In other words, a hammer forged barrel is squeezed into shape by immensely high forces over a mirror image of itself, and is thus less likely to have variances in rifling twist rate or chamber dimensions.

This is somewhat true – some manufacturers do forge rifling and chambers with one mandrel, in one process. Others forge the rifling and then ream the chamber as a separate process, much like it would be done after cut or button rifling processes. I have observed seven hammer forges in operation, and discussed the pros and cons of both methods with a number of gunsmiths, engineers, technicians, and machinists in the United States and Europe.

This hammer forged barrel cutaway has had a mandrel section placed inside the chamber to show how the barrel steel is “squeezed” over the mandrel during hammer forging.

Companies like Beretta value the hammer forged chamber and rifling because it eliminates the inconsistencies – both in the “length” of the chamber and the alignment of the chamber with the rifling, which can suffer based on the quality of the employee performing the work – that result from performing the process separately. That said, they don’t use this one-step process for every barrel they make.

On the other hand, Steyr, which has been hammer forging barrels longer than any other company, reams chambers in a separate process, in part because there can be issues with the way the barrel steel “flows” around the neck of the chamber, negatively affecting accuracy. Steyr’s focus is on precision, and employees take their time ensuring that each barrel has been forged exactly right, and each chamber has been reamed – and then polished by hand – correctly.

At this quality control station, a Steyr employee points out the standards to which each Steyr barrel is held during production.

Both companies – and many others – put out fine products. Unless you’re just looking to buy a rifle and don’t really care how it was made, you would do well to research how the rifle you’re considering was manufactured, and what the manufacturer’s intent was when making it – long barrel life? precision/accuracy? reduced manufacturing costs? – and ensure that those goals match your own.

Summary: Hammer forging chambers can help ensure that they are dimensionally correct, but so can a skilled and careful machinist with a reamer.

Which Ammo or Chamber Should I Buy?

It’s a good idea to have an understanding of all of the factors regarding this issue – and what you will use the rifle for – and make a purchase based on this knowledge. With that in mind, here are my thoughts on the four chamberings I’ve discussed in this article.

.223 Remington – Because it’s the only SAAMI standardized cartridge, it’s the only one you’re likely to find used in rifles produced by major manufacturers. I would prefer any of the other three to “regular .223.” However, you will not be at a huge disadvantage as long as you buy mostly .223 ammo. As stated above, you are not likely to encounter major problems with limited amounts of 5.56 in a .223 rifle fired out of necessity or in an emergency. Doing so at a high volume for the long term is probably not a good idea. In terms of a carbine-style AR-15, I see absolutely no reason to purchase one with a .223 Remington chamber.

.223 Wylde – Produced by a variety of smaller manufacturers, .223 Wylde can be an excellent choice if it is executed properly. I have personally had overpressure issues with improperly reamed .223 Wylde chambers. I’ve also had excellent accuracy and no pressure signs with 5.56 from properly reamed .223 Wylde chambers. As always, buying a quality product is often the best way to go.

5.56mm Noveske Match Mod 0 – Similar in concept to .223 Wylde in that it attempts to strike a balance between pressure and accuracy, it has the advantage of being produced only by Noveske, a shop known for precision and attention to detail. All of the Noveske barrels I’ve owned – about a dozen – have delivered accuracy, precision, and safe, reliable function. This comes at a price, for Noveske barrels are not cheap.

5.56mm NATO – The best bet for those looking to shoot high volumes of 5.56mm ammunition without an emphasis on tack-driving accuracy or precision, 5.56 barrels from reliable machine shops will outshoot most humans while also keeping pressures within normal limits. Cheap 5.56 barrels often disappoint.

Summary: Buy a well-made rifle with the chamber you want based on your needs, shoot the right ammo in it, and have fun. For most people, especially those not sure of what type of shooting they’ll be doing, a 5.56mm chamber is the best all-around choice. It is my fervent hope that this article has helped you better understand the topic at hand.


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Leave a Comment Below

  • Chuck Reynolds

    wow.. very in depth. well done kids. :)

  • Rodger Young

    finally, thank you, I’ve gotten so tired of the expertitis shown on some sites.

  • Rodger Young

    Oh, any chance of you investigating 7.62 NATO v..308 Win too?

    • Ryan J Peterson

      I’d love to see that

    • Nathan Tramp

      Oh yes. Not only would I read that, but I’d pass it on to my buddies at the range. Wherever an issue requires both chronographs and micrometers, conventional wisdom holds no positive conclusions. :-)

    • Jack Mehouf

      Only difference is the 7.62×51 NATO is rated at a lower max pressure then the 308 win so you can shoot 7.62×51 NATO in any 308 chamber. Call the manufacturer to see if you can shoot 308 win in a 7.62×51 NATO chamber. The answer will more then likely be yes.

    • Andrew Malaxonis

      That’s easy everything just in reverse .308 is higher pressure then 7.62
      nato

    • Robert Acord

      Glad to see I am not the only one on this

  • Paul Lombardi

    Great Job… Are you sure it’s your 1st lab report.

  • Gunmart Blog

    Well done, Andrew. That article is a wealth of knowledge.

  • Jeff Acheson

    “That said, one noted gunsmith told me about a test he had heard of, conducted by an ammo manufacturer, in which 5.56 in a.223 barrel exhibited pressures of 77,000 PSI.”

    Sounds like someone fired a M197 proof load in a.223 barrel.

    • Scott Esse

      no it only means that a tight chamber, most likely set up for target shooting where the bullet engaged rifling as soon as the bolt closed was present

    • Richard Schurman

      Scott Esse I did have a question that was not answered and that is at what point should you replace a barrel? Based on this article if you shoot both types of ammo the barrel should fatigue sooner due to heat and pressures. What’s your thoughts?

  • Joe Cargyle

    awesome, finally something I can refer to that has tests and results based on scientific study. thankyou so much.

  • Steve Beasley

    Great job! I have an older mini-14 that says.223, but according to Ruger, it’s actually chambered in 5.56. He stated that “Ruger Mini-14’s have 5.56mm chambers and are designed to use either 5.56 or.223 factory ammunition loaded to United States industry specifications except in the Target model.” Thanks.

    • Jack Mehouf

      Your right but for a little more information, the wording on the barrel is the most important part. The mini-14 says .223 cal not .223 rem the same goes for any other .223 cal marked barrel.

    • Scott Esse

      INCORRECT! .223 refers to .223 Remington, NEVER assume otherwise. ALWAYS look to the weaker round.

    • Richard Schurman

      Thanks for that ‘pearl’. I have a Mini and ARs and was curious about that very issue and Scott backed you up (He knows his stuff). Unfortunately that was not covered in the article in spite of the number of Minis out there.

  • Keith Finch

    Very well written

  • Jerry Nicholopoulos

    thank you for a very well written informative article its good to see facts stated instead of opinions. clears up some questions I had ass I have both 223 and 5.56 rifles.

  • Vince Miller

    Well done! I have long suspected this to be the case!

  • Ryan Linwood

    Never imagined my preferred ammo vendor would also become a source for deep dive ballistics analysis. Great article and I hope this continues.

  • Aaron Weeks

    Great article! I always enjoy reading your stuff, so please keep it up.

  • ArmsVault

    Great article, Andrew!

  • Bill Sewell

    Exceptional article, sort of what I would have expected. Manufactures have for many years been careful about loadings that can be chambered in different firearms.

  • Ronnie Schille

    Very nice article….. Bottom line… AR-15 rated for 5.56 & 223, use either or bc its rated for a hotter round… So if we are playing reach out a touch somebody at 550 yards of accurate fire… Load the nato, if your going to be close quarters less than 150 yards, 223 all day.. very informative… Thanks for the info, I am deff going to share this to all the people who have “attempted” to inform me about shooting 223 out of my AR-15.

    • Jeff Cash

      I had often wondered why my factory colt ar15 had both 223 & 5.56 stamps and just assumed that the differences were insignificant, if any at all.

  • Tom Smith

    Building my first AR and this was a GREAT article to help me confirm what I already had suspected. GREAT JOB!

  • Alan Sims

    I am pleased that I finally read a truly informed opinion!

  • Randy M. Griffin

    very interesting article. I always wondered how the pressure difference’s would line up with the.223 and the 5.56 x45 would come out on paper….Now, what do we do when the gun treaty steps in and starts taking our guns. Would anyone in here support the UN’s action’s if they started coming into the US and started taking guns from Americans with this treaty? I think there should be a discussion on that topic…

    • Scott Esse

      Seek a psychologist for that streak of paranoia, If you really think the people will let that happen

    • Randy M. Griffin

      Scott Esse You are quite the A$$HOLE are you not?…What I said was just a way of getting regular people to think about the UN and the treaty that was signed…And you have to come along and start with your BS and telling someone you don’t even know to seek a psychologist….Grow up…..

    • Scott Esse

      YOU are the Adam henry, little boy, you got your answer and didn’t like it so you resort to vulgarity. you are just a half step above a liberal, if you cant handle it stay off the internet and you wont get butthurt,

    • Randy M. Griffin

      Scott Esse Any time you think you can hurt me, just have a try at it…You will find out how hard that will be…Any time, LIttle Boy…You act more like a liberal than anyone in here…

    • Randy M. Griffin

      We aren’t that far apart…Want to meet up sometime? I’m game, are you?…

    • Randy M. Griffin

      Scott Esse I’m not hurt at all..Would you like to take me up on the meeting me in person? I will await your response…I would really like to meet you and see what the outcome is..And you act more like a idiot progressive, more than I have ever seen on this site. I am pure conservative and lets meet and see. And if you didn’t act like an A$$hole, then you wouldn’t get called one…And I will lay odds that I own more guns and ammo than you ever dreamed of having…like I said, I am a true conservative and I am prepared for what comes…

    • Randy M. Griffin

      Scott Esse And this is the last time I waste my time talking to someone who hasn’t got a clue. So I will write anymore about this stupid subject…Either meet me or don’t keep this stupid junk up..

    • Richard Schurman

      Scott Esse You can’t fix stupid so I encourage not to even try since liberturds are just born that way.

  • Gregory Garland

    Great article. Thanks for writing this. I suspect the secondary spikes are due to too slow powder for that application.

  • Mark J Modlin

    Excellent article, analysis and data. Todd check this out.

  • Mike Thomas

    Just the article I needed to get my project underway with some reasonable idea of what reamer to order.

  • Ronald Grapes

    You supplied the info that I was interested in and now am aware of the differences. Very interesting article,
    Thanks again

  • Stacy Lawhorn

    So, stupid question. Can you fire.223 in 5.56 barrel?

    • SharonAnne Stinson

      Yes.

  • Stacy Lawhorn

    So, stupid question. Can you fire.223 from a 5.56 barrel without any problems?

    • Gordon Cataldo

      yes, 223 has lower pressure so wont hurt the firearm and should cycle fine

  • Cameron Ford

    Glad I went with the 5.56 NATO.

  • Carter Fairbanks

    Well done, thank you.

  • Phil Rains

    Elexcent Artical. Thanks.. A question please…… What do you think of WINDHAM WEPONDARY?

  • Bill Gridley

    Had a Mini 14 and a Remington 788 for years but haven’t shot either much. Last year I took them out and so many rounds would not chamber in the 788. So I laid them to the side and kept spent brass separate. Then I loaded rounds that would not chamber into a mag for the Mini-14 and all rounds fired and ejected. I glanced at the next bench over and saw an AR and boxes of 5.56. I realized I was shooting a mixed bag of.223 and 5.56. 5.56 would not chamber in the bolt action. OK. I need to sort my rounds. Thanks for your info.

    • Scott Esse

      There is NO (ZERO) physical difference in the SIZE of the rounds so if some would not chamber in the 788 you had other issues going on since it is more forgiving than the semiauto Mini-14 is.

  • Bob Whitney

    Thank you for your considerable effort and clear communication

  • Timothy Clifford

    Well done sir! You have just given me a place to send all the “no, no, I know better” discussions that come my way. Bravo!

  • Lamont Andrews

    Im reloading new 5.56 nato casings. Im also having a hard time finding reloading data for the 5.56 nato casings. Should I use 223 REM data? Do you need more or less power in a 5.56 nato then a 223 REM with the same bullet?

  • Joe Wiseman

    Great article, really enjoyed it. Well done!

  • Charles F. Easter

    Great story, thanks!

  • David Johnson

    Great article. Thank you

  • Christopher Blake

    Fascinating article. Deduction: Don’t worry, be happy. I agree, I’d love to see that same comparison on.308 vs 7.62×51.

  • Jack Rowland

    thank you for this info it was very informative.

  • Sean Verwold

    Very nice and informative article on the 556/223 topic

  • Randy Cohen

    Thanks for a great and informative artical I have an older Ruger Mini 14 handles both with no problem.

  • Tom Driscoll

    Thank you for the time and effort used to produce this report. I greatly appreciate the information.

  • Pat Cavanaugh

    Very good article with great research. Thank you

  • Chris Ruten

    Thank you! Well done.

  • Logan Molina

    Very informative.

  • Mike Richardson

    Great article with lots of technical information at a level that we normal humans can understand. I found it to have been the best explanation on this subject to date for me. Great job.

  • Fred J Meier

    Excellent article – professional journal caliber! Thanks for making perfectly good sense out of common sense.

  • Ed Taft

    Would there be a difference between older (preban) weapons and the newer ones?

    • Scott Esse

      TIME

  • Bob O’Brien

    Very informative–thanks

  • Del Brunning

    Thank you for all your hard work on this very informative article.

  • Charles Thomas Shaner

    I knew it all along that it was just a slight difference of a little more powder and wouldn’t hurt my Mini 14. Ruger makes an excellent firearm their 10/22 is also a great 22 in which you can shoot long or short rounds regardless if it states it on the barrel or not. Awesome article, Proof for the Nay Sayers;).

    • Roger Neer

      My personal opinion,The mini 14 will shoot anything…. But thats open for opinion???

    • Scott Esse

      Per Ruger AND printed ON the instruction manual of the mini-14, the rifle is designed to shoot both 5.56 and .233 ammunition. If you do not have your instruction book you can download one from Ruger

    • Richard Schurman

      Scott Esse <- You Da Man Scott. Thanks for your 'pearls' on the Mini14 and the Weatherby issue. I had read that very issue about bpore techniques in an article by Weatherby so I am surprised after all the "research" the author did not discover that since I am just a plinker and I found it. I think I will follow your info. Thanks

  • Frederick Palmer

    Great article, cleans up a couple of urban legends on this issue.

  • Jerry J Rivas

    Well written, and well researched article.

    • Eric Morris

      Good article. Finally something other than a “what’s your favorite color” post!!!!

  • John Ferguson

    good info, thanks!

  • Marty Fry

    Thanks for your time and efforts, I too would be interested if you find the time and energy in a 7.62 vs. 308 challenge.

    • Scott Esse

      There is virtually no difference in 7.62×51 and the .308 Winchester. If you research these caliber designations you will find them both marked on a large number of commercially produced ammunition packages both imported and domestic, and the third party testing puts them both in the same pressure classes, unlike the 5.56/223 situation which seems to be unique in this issue. Part of this is due to the use of an “off the shelf caliber” that has grown I popularity as a hunting round substantially more than the .223 has, where as the 5.56 has seen its popularity rise due to the military rifle design rather than the caliber itself becoming the popular item. In short there are more bolt action and civilian looking 308 rifles out there than military looking (M-14. M1A1, AR-10) where as the opposite is true of the .5.56 class rifle with the ar15 being more popular than any other design 5.56/.223, since there really are better caliber choices for hunting in this class caliber range, from the .22-250, on through the various 6mm rounds including the .243 and up to the 6.5mm including the 270…

  • Tim Hogg

    I know thus article is more than a year old, bug I would like to see something of this detail discussing barrel twist for this caliber please.

    great write up, and thank you!

  • Vernon Russell

    Wow. What an article. While I did not really understand much or any of the real technical data I did appreciate the time and effort that was taken to not only perform the tests but to write it in such a way that I think I understood. Maybe? I liked the bottom line. Basically what we have always been told, shoot what it was originally designed for except in emergencies. Thank you.

  • James Broyles

    Good article

  • Rich Robinson

    I just fired both rounds described hornady.223 next to a nato federal 5.56 both 55g fired out of a new windham ar 15.Dont need no instruments but sound and recoil there is a noticeable differenc.The federal 5.56 55g and the 62g felt similar but when firing the hornaday .223 it felt and sounded more like a 22 compared to the nato rounds.The hammer didn’t even lock back after the last round.

  • David Willson

    Before purchasing my rifles, I contacted the manufacturers and asked if their products handled either one or both cited cartridges. Some said Remington .223 only, and others said theirs were MilSpec and rated for 5.56 and therefore could handle either. MilSpec was good enough in combat, so that was they way I chose. :-)

  • Douglas Lohr

    I thought that there is a difference in the rifling between the two calibers. One squeezing into the rifling and the other opposite.

  • Ron Spicer

    All I want to know is, does the 223 yaw and fragment when it hits soft targets like bad guys??? I want a bullet that does maximum damage to buy guys. If the 223 can not do that, then all I want is 5.56

    • Brad Lomax
    • Scott Esse

      You have been listening to way too many myths and stories on the 5.56 round. Every Round can do this, BUT it is dependent on many different things such as velocity bleed off anatomical structure hit and so forth. What you NEED to do is start visiting HUNTING forums and start studying the bullet performance threads. You will find that the most EFFECTIVE projo is one that does NOT fragment at all, maintains ALL of its bullet weight and MUSHROOMS out to about twice it’s original diameter, thereby delivering maximum terminal ballistic performance Small amounts of damage from fragmented small rounds have minimal over all effect on bringing down an opponent. The BRAIN must be caused to stop functioning. Center of mass is the largest target, the brain is relatively small in comparison since the area that needs to be destroyed to stop an opponent is only 1/4 to 1/3 of it’s size. So the COM needs the BIGGEST hole to cause the most and fastest blood loss possible, Fragmented bullets cant do this. Like I stated Start researching bullet performance in hunting forums, where this fact is proven regularly with living targets and real world experience proves what works and what doesn’t.

  • Stephen Emert

    woodenflutes
    I have a Colt AR15 and I have yet to shoot 5.56 ammo thru it. I ordered 5.56 FMJ and was hesitant about shooting it thru my AR15. This test and the results certainly proves that the 5.56 is not going to kill me if I shoot it in my 223. I was wondering how I was wondering how to rid myself of 420 rounds of 5.56 and get my money back. I will try it first because like many of you I was concerned and now I am a little more confident. THANKS Lucky Gunner for being the type of people willing to help others.

  • Stephen Emert

    Stephen Emert
    I have a Colt AR15 and I have yet to shoot 5.56 ammo thru it. I ordered 5.56 FMJ and was hesitant about shooting it thru my AR15. This test and the results certainly proves that the 5.56 is not going to kill me if I shoot it in my 223. I was wondering how I was wondering how to rid myself of 420 rounds of 5.56 and get my money back. I will try it first because like many of you I was concerned and now I am a little more confident. THANKS Lucky Gunner for being the type of people willing to help others.

  • David Farber

    Great Article which enlightened me a lot, thanks.

  • Dwayne McCullough

    Seriously great article backed up by empirical evidence not hearsay! Thanks for putting the effort into this and slamming the book shut on this topic! Posting a copy of this on the range’s cork board.

  • Donald Amerman

    I work with the AR15 platform all the time at work and have attended the Colt armory school several time and the advanced course as well. I was enlightened of Michiguns products only recently by Dean Caputo of Colt. My Department has a bunch of older Armalite rifles with very tight chambers. when these rifles are pushed using 5.56 ammo they get heated up they will blow primers and start failing to extract. using the michigun reamer this problem disappears!

    • Scott Esse

      This is an issue that Weatherby had when developing his high pressure namesake magnums. He solved it by free boring the chambers, (an extended chamber throat before engaging the rifling) which is now done on ALL Weatherby rifles. Unfortunately The author wasn’t aware of this and any data derived with his Weatherby or compared to it is moot because of it. This is sad because the disqualification throws the types of explanations out, when so many shooters would have benefitted from them had the proper data been used. Instead of comparing a true .223 chamber to a 5.56, he was effectively comparing a 5.56 to a 5.56… Rule number one, When comparing chambers ALWAYS make accurate castings of them FIRST so that you can measure them and not depend on supplied information. The real world doesn’t exist on paper, as you found out with the older Armalites.

    • Rodger Young

      Sounds like Oak Park PD, they went through an extensive test to figure out their undersized chambers.

  • Paul Harrelson

    The first AR I built I ordered a high quality heavy barrel .223 with 1/10 twist, at the time being ignorant of the difference in chamber dimensions, the manufacturer recommended the 1/10 for the .223. Mounted a Shepard scope and headed for the range…. The 62g SS109 would keyhole, and sometimes not even hit the target at 50 yards, however with the 55g Remington I was getting quarter sized groups at 100 yards. Not really sure if it’s the rifle twist ratio or the chamber dimensions that make the difference, my Colt AR shoots both SS109 and .223 fine, but not near the accuracy that I get with the custom heavy barrel with 55g Remington .223 velocities ranging from 2900 to 3200 not seeming to matter….

  • Ernie Fernandez

    Now I know!

  • Jackson JJ Crisp

    Thanks for the info, very professionally done, with lots of facts.

  • Tim Wilson

    Great article, I found it very helpful in my choice for my first ar build…thank you

  • Paul Baratti

    This is pretty much what I’ve found to be true. After firing both and talking with others, mostly former Marines the verdict was the same. 5.56 is a good all around choice for someone who doesn’t do match shooting but wants a firearm that performs well in various, and unknown conditions and situations.Now can he answer the next question, 1 in 7, 1 in 8, or 1 in 9…

  • Ben Silvey

    Would like real input on the best rifles, I’ve heard all kinds, but I want a dependable accurate gun into the 5000 round range at least, hears Lwcr is the best?

    • Scott Schoemann

      Any such commentary would really be moot since it would be based on opinion of a rifle made at a specific time. Since every major name AR manufacturer purchases parts from contractors and none make 100% of the components used in the rifle, the perceived quality will vary from batch to batch and year to year. The only way to avoid this is to build your own or pay someone else to do it for you, where you specify every single part. However, since you are talking about a projectile that is only .224″ in diameter and a maximum weight of 79 grains when you CAN find them, and a BC of approx. .396, it is a total waste to go so far overboard in building such a rifle unless you are shooting for money.

  • Scott Esse

    You used the Weatherby rifle as one of your examples. Sadly this disqualifies Every single bit of information that is derived with and in comparison to that particular rifles results, as well as your techniques and methods due to your lack of knowledge. Weatherby “free bores” their rifle barrels. This effectively lengthens the chamber before the bullet engages the rifling, REDUCING chamber pressure substantially. This fact is well known within the industry and your lack of knowledge of it disqualifies tour entire treatise and sheds doubt over the rest of your work in this subject, Sorry but you did this to yourself.

    • Will Early

      In theory, yes. However, wouldn’t losing the 5.56 into the weather chamber draw a parallel between calibers in the same rifle rather than the cartridge itself, the point of the entire article?

      The cartridges fired from their respective chambers initially were to measure baselines for not only safety, but the second phase.

    • Will Early

      Let me try that again without typos and auto correct.

      The initial test was to establish a baseline between calibers (and confirming pressure safety parameters) into their respective chambers. The second phase was switching up the calibers, to see how one cartridge would behave in its sisters chamber. What’s the problem?

    • William A. Roderick II

      That is true about Weatherby Magnums, but their Vanguards in standard calibers would use SAMMI chambers.

    • Dylan Bland

      That was my assumption too. Vangaurd is a howa basically. Surely not freebored. I’ve not checked into that, but i have heard of sub moa vangaurds. I’m not a weatherby fan, so I’m not up on them, but that statement alone leads me to assume they are not free bored.

    • Joshua Murch

      Assuming a absolute zero is possible. But it is also common knowledge that no chamber is exactly the same. Why dont you go do your own testing

  • Jason Johnson

    Outstanding article with well done fact over fiction evidence. Any serious shooter knows that accuracy of information leads to accuracy in shooting. Thanks for the excellent info.

  • Peter Topjian Sr

    Very good explanation of the 556mm an 223 cal like u said. Buy a rifle we ith markings on it 223 an 556 mm be safe!

  • Paul Williamson

    Thanks for the information.

  • Wayne Adkins Jr.

    everybody that’s been in the military knows the difference and & M 4 which is different from an AR can shoot both calibers thank you..

    • Mike Baber

      I’ve had a few M4’s, currently shoot a Bushmaster M4A3 and they’ve All shot both 5.56 and .223.

  • Kody Rudder

    Thanks for the info I have always shot either load in either caliber

  • Robert Mills

    Great article. Thanks for the resurch.

  • Steve Coyle

    Thank you, does a fluted bull barrel make a difference. In this difference.

    • Scott Schoemann

      none what so ever, the fluting is external to the barrel, and has nothing to do with the chamber or rifling. All it does is takes a bull barrel profile and lightens it by selectively removing portions of the barrel (flutes) running the length of the barrel, while maintaining the majority of the strength od the barrels original diameter

  • Frankie Roberts

    Impressive. I hope you get paid for your reasearch. Lots of complicated info covered very well.

  • Alan E Jackson

    Very informative thanks

  • Gary Fowler

    You people do realize that the guns that are chambered for the .223 are usually either identical to those marked as 5.56 (typical at) or of significantly stronger design capable of shooting cartridges with higher pressures than the 5.56 (typical bolt action).

    These numbers may be technically correct, but they ignore basic common sense and mechanical/dynamic physics.

    • Gary Fowler

      Edit: (typical at) should have been (typical at).

    • Gary Fowler

      Typical AR

      Smh…

  • Jim Gipe

    I shot 5.56 in my ruger .223 and it blew up. Not the first time I had used 5.56 ammo. Thank goodness the action held together for the most part. It broke the stock into and blew the floor plate down. There was another case reported to our local gun shop but I have no info on which rifle just that it happened when 5.56 ammo was used in a .223 rifle. Best advice is to only use ammo that matches the stamp on the barrel

  • Christopher Fred Tafel

    I fire both .223 and 5.56 out of my .223 barrel of my saiga .223

  • Todd Tardugno

    Very interesting. I am so glad I read this thoroughly. Definitely dispelled some myths for me.

  • James Salter

    I have a mini 14 and I called the manufacture of Ruger and they told me that you can fire a 5.56 and the 223 Remington that it was safe to fire either one.

  • Eddie Van Winkle

    Thanks for the very informative article. I have an M&P 5.56 Nato I’ll be in good shape either way Thanks…

  • Scott Arnold

    thank you I learned a lot

  • Rebecka Dornn

    I don’t get why everyone compares an apple to an orange. And say the have answered the eternal question. If you were comparing the 5.56 nato XM 193 to the .223. Would be an appropriate comparison. Maybe someday I will come across a trully enlightened comparison. As of now I am still looking for true facts on both calibers. And if you really spent that much time researching this artical. You are a bigger procrastinator then I. As it reads like a rehash of others work.

  • William McKenney

    I pulled the bullets from 50 ea 5.56 rounds with lake city 69 head stamps. I weighted each powder charge carefully. Results were 23.5 to 28 gr. Could be inconsistance charges are the problem and not chamber dimensions. I have fired thousands of military rounds in my Herters bolt action .223 before I was aware of any warnings, never had a problem. Thanks for a great article. Bill

  • Eric Dominie

    Very well written and informative! Lots of very good information for people not familiar with .223/5.56mm

  • Greg Garrison

    Am I the only person who read these comments and thinks scott esse is jealous of this author and should go write his own article? Damn he’s annoying

  • John S Clary

    Well said thank you I have been saying that for years 5.56nato is no more than a 223+p

  • Christopher Waine

    Great article. I have been a fan of the 5.56 Nato and AR15 ever since my time in the service. I am curious though if the difference does not have to do with weapon performance and recoil. It seems that muzzle velocity is consistent when using according to the charts .223 and 5.56 in a 5.56 NATO barrel. The only change according to the chart is pressure. I am curious if the additional pressure when using 5.56 in a 5.56 barrel is to ensure proper mechanical function of the bolt. I am curious if a double feed would occur more frequently when using a .223 when laying down suppressive fire. Lower pressure might reduce recoil and result in better repetitive fire accuracy. I am also curious how the .223 and 5.56 rounds stack up when it comes to energy at the muzzle and again at 300 meters.

    Thanks a bunch,

  • Dave Bennett

    Thanks for sharing. When i have more time I’m going to read it all. My AR is stamped on the barrel it will shoot both. Looks like an interesting read.

  • Don Sprecher

    I would be interested in reloading .223-5.56 info. I have a 5.56-.223 upper receiver, and have been reloading .223 for years with excellent accuracy.
    I hunt predators with my handloads. I use an RCBS electronic powder measure, I resize and trim every case by hand, use same primer ,and use a hand primer, and I neck crimp every load by hand. My hand loads are exactly the same, and every round proves it at range in accuracy, and on the chronograph.
    When I load 5.56 cartridges, I have found the only safe way to reload the military brass I have, is clean the primer pocket and clean the primer crimp to accept the primer, and resize them as I do the .223 cartridge.
    As far as powder charge, I reduce my powder amount by 10 percent to avoid excess ressure.
    I do this because the military case walls
    are thicker. And my loads are safer. My accuracy hasn’t suffered.
    I also keep the .223 reloads separated for hunting and defense,
    I load the 5.56 brass with fmj bullets for the range and drills.
    As stated before, I keep both .223 and 5.56 cases separate.

  • Christopher Sopko

    Great job on your research and testing. The ammo variances was very interesting with the machine tolerances of the barrels tested. Your absolutely right on quality of barrels making a difference accuracy. Thank you for well done research that you presented. Chris S.

  • Dodger F Baybeh

    5.56 nato is 5.56×45 my barrel is marked 5.56 nato basically I’m good with shooting both 5.56 and .223 or should I only use .223 I ask because of all I ever used was only .223 not that I have a barrel that reads 5.56nato I’m fine right is that accurate or is there ammo that I need worry about if so I’ll continue .223 that’s what I purchased first and fired first out my rifle until I noticed 5.56 nato while cleaning it is it safe I don’t want a blow out

    • Jeff Blinkinsop

      If you have a 5.56 barrel then you can shoot whatever tickles your fancy. I tend to stick with 5.56 as much as possible but .223 won’t hurt it and sometimes its all that you can find and its cheaper.

  • Bill Fair

    nice write up, too bad I cannot share it to my friends on facebook!!!!! those that use these cartridges………

  • Sharon Deweese Davis

    This is perhaps one of the better articles discussing subject of .223 vs 5.56 ammunition. The diagrams and videos added to the information covered.

  • Sean Boyd

    Parts of my brain are oozing out of my ears. As a relative noobie to this sort of thing, I just learned WAY more than I thought I would need. Evidently, I needed to know more. Thanks for the article.

  • Troy Williams

    Excellent article which backs up my real world experience with these cartridges. Of course many regard “real world” as simply anecdotal and then have their horror story, which happened to a friend of their 2nd cousin’s boyfriend…

  • Mike Sullivan

    Great article… well researched and well written

  • Gabriel Uhrich

    Thank you for taking the time to do the research and testing and then write the article. It was informative and interesting.

  • Jeff Myers

    After all said and done just stick to the what the was gun was designed for.