223 vs 5.56: A Quick Comparison

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June 2, 2021 / Comments (16)

Guns & Ammo

The difference between 223 vs 5.56 is mentioned all over the internet. However, the sad part is that most of the information provided is either wrong or misguides the reader and does not answer the question. So today, let’s discuss the real differences between the two.

RELATED: Ammo Review: Federal American Eagle .223 FMJ

223 vs 5.56: Which Do You Need?

The significant difference between the two is that 5.56 has a higher pressure level, which runs at just about 58,000 psi. However, a 223 Remington runs at approximately 55,000 psi.

The Basics

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Both the terms 223 and 5.56 refer to the caliber of the rifle. The 5.56 started off as a military cartridge in 1950 and was technically called 5.56x45mm NATO. However, by the 1960s, Remington decided to release a much similar cartridge, the 223.

Since the release of the second cartridge, people have had difficulties in determining the difference between the two. However, due to a lot of research, you can now find the answer to this on many platforms.

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223 vs 5.56: Measuring Pressure

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There are various ways to measure pressure; the oldest form of doing that is the copper crusher method. In this method, a test barrel would have a hole drilled in it. After this, a small copper cylinder had to be over the hole. A round would be fired to hit the copper cylinder, and by doing so, the copper cylinder would compress. A measurement of the cylinder’s length before and after would determine the peak pressure.

This is known as the copper units of pressure but is now more commonly known as PSI. Through this method, measuring the difference in the pressure of 5.56 and 223 made it easy to conclude that the 5.56 has a much higher PSI than the 223.

This is the most significant difference between the two as one has more power than the other.

223 vs 5.56: Ammunition

Both ammunitions have a different look, and you’ll notice the difference if you put the two side by side. Here are the two significant differences between the two ammunitions:

  • On the case rim, a “223” is stamped on the 223 Remington brass, whereas the 5.56 NATO brass may only have a date, initials (Ex: FC), and one or two more symbols.
  • On the case rim, you’ll also notice that the 5.56 military ammunition will have a crimp around the primer pocket. However, not the cases hand loaded in the civilian market.

Issues with the Differences

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Since both are cartridges, the primary issue that comes with these differences is that when firing a 5.56 NATO cartridge in a rifle chambered for 223 Rem. Due to a more extended throat of the NATO chamber, this combination will cause a 223 chambered weapon to run at 10,000 psi higher than its usual 55,000 psi. This is most certainly not safe as this can result in harming the operator or even rifle.

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223 vs 5.56: Similarities

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As they both have numerous differences, they also have a bunch of similarities, which is generally the reason why there is confusion when comparing the two. Here are a few similarities that you might notice between them:

  • Both have the same external case dimensions. However, shoulder transition may be of a different radius.
  • The length of the cartage is the same.
  • Same case trim-to length
  • Initially crafted for 55-grain bullets.
  • They both use a small rifle-size primer.


Watch this video from Gavintoobe as he talks about the facts and myths about the .223 and 5.56:


Which do you prefer?

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Understanding the difference between the two is essential so that if you ever plan on buying one of them, you’ll know which one to buy.

We hope to have answered some of the most commonly asked questions regarding this topic!

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16 Responses to :
223 vs 5.56: A Quick Comparison

  1. Lloyd Plett says:

    I’m unsubscribing. Reading your articles makes me dumber. Do some real research before writing. Much of the “Info’ in this article, as well as others from this site, is simply incorrect. Not very well presented, either. I seldom flame others, but you have earned it.

    1. Thomas Woodcock says:

      I have an ar15 20″ barrel 1/9 twist
      Barrel doesnt indicate .223 or 5.56
      How do i know which one to use?

      1. SHAWN says:

        Most ar15 rifles will Handel both the 223 and the 556 , if the barrel is stamped 556 then you can shoot both 223/556 . If you have a barrel that is stamped 223 then you can only shoot the 223 ammo .

        1. SHAWN says:

          I didn’t notice that you said yours isn’t marked , iit is probably set up for 556 but i can’t say that for sure so if you want to be on the safe side shoot the 223 , as the 556 barrel can shoot both but a 223 barrel can only shoot 223 .

          1. Anonymous says:

            fyi. I called Ruger about the difference. They said If it’s the thin barrel you can safely fire the 5.56 in Mini 14, but not the heavy barrel.

  2. Thomas Woodcock says:

    I have an ar15 20″ barrel 1/9 twist
    Barrel doesnt indicate .223 or 5.56
    How do i know which one to use?

    1. Yosemite says:

      Thomas Woodcock

      Is the weapon a new one from a known name brand ?
      OR
      Is it one that someone built?

      IF a name brand bought in a store: The caliber will on the Left side of the lower receiver.

      REMEMBER: Anyone can change out the upper or lower…..and even change calibers such as .300 Black Out or others

      IF it is not on there, the best information I can suggest is to take it to a gunsmith.

    2. Sotia Phan says:

      223 to be safe until you break the barrel down to take a look and confirm

  3. John says:

    With all the mis-information about these cartridges, I think it would be helpful if you guys had actual pressures of both from the same BBLs using the same measuring devices. Saying that the NATO chamber is slightly longer doesn’t cut it. the Wylde chamber is longer, too. How much ‘longer’ is the NATO chamber? How much longer is the Wylde chamber? What are the dimensions of the 223 that (theoretically) make the pressures spike? If I shoot a 223 in a NATO chamber, how much pressure do I lose? How many FPS do I lose. What is the accuracy difference at 100, 200, 300 yards?
    You’re supposed to be the ‘experts’. Give us ‘expert’ information…
    “Inquiring minds” and all that…

    1. Josh says:

      The “longer” chamber of the military chambered 5.56 is due to the shape of the M856 64grain tracer. The olive of the bullet is forward of the ogive in the M855 ball bullet. This is because the incendiary required to make a tracer takes up space that lead can not. So the lead core was elongated toward the front of the bullet. I have done actual testing of both 223 and 5.56 in the same barrel and got a whopping 17 psi difference between the two. The disparity in the published numbers is because the military uses a different method of pressure testing than SAAMI. Both will run in any well made firearm.

      1. Anonymous says:

        Josh did his homework. Absolutely correct.

  4. Jeff Howlett says:

    Buy a new one and use what the salesman at the counter says to shoot.

  5. Laurie W says:

    I don’t understand why you all think you need rifles like this. To me these should only be owned by law enforcement and military personnel. I am not against guns don’t get me wrong, but with guns like these to me you are either in a gang or looking for trouble. Some of you may only want them just to have them but I don’t think they are necessarily a gun you should have as an individual person owner. Sorry just my opinion. But not against hand guns and regular rifles.

    1. A Patriot says:

      Total woman moment. 😑

      The reason you’d want to and SHOULD own something like an AR15 is BECAUSE the military/law enforcement has them. I’m sure in your mind you can’t possibly fathom that authority might turn on average law-abiding citizens, but it has and likely will, in the future, happen. You must not be keeping up with the news, but maybe you’ve seen the nazi-esque Covid camps that have been opened in Australia? Guess who’s forcing people into those: law enforcement. Cops have also been seen recently attacking people protesting the lockdowns. Can the Aussies do anything about it? No. Because they don’t have guns and the cops do. The new governor of NY has announced that she’ll be replacing nurses in hospitals (that have been fired for refusing the vax) with military personnel, who will be ordered to administer the jab to people, possibly forcefully, in the future.

      The 2nd ammendment isn’t for hunting or even self-defense, as many uninformed idiots will tell you. It is there to ensure that the common man has an option to take back control of the nation should a tyrannical power oppress them. And I mean ACTUAL oppression, not something gay and fake like “tHe GeNdEr PaY gAp” or “sYsTeMiC rAciSm”. You should participate in and actively encourage the ownership of weapons like AR15s, AK47s or any high capacity, semiautomatic rifle.

      Because one day you might need it when your Glock just won’t cut it anymore.

    2. Major Ima Headache says:

      Why do you need such a ubiquitous vagina? Only whores and supermodels need such things. Wouldn’t a normal vagina do for your needs? With a vagina like you insist on wielding, you must either be in a harem or wanting to get “in trouble.” Beautiful vaginas should not be had by normal people–only the elite. Sorry, just my opinion.

  6. Mick says:

    My question that I’m having a hard time finding an answer to, is the difference in accuracy. If my AR barrel says 5.56, and I fill 1 mag with 556 and another mag with 223, and I shoot both of them at the same 100 yard target, how much difference will there be in accuracy? Would I need to re-zero in between switching?

    Thank you.

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