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5.56 vs .223: What's the Difference & Which is Better?

5.56 vs .223
August 24, 2021 Edited March 17, 2023 8409 view(s)
5.56 vs .223: What's the Difference & Which is Better?

Why the Difference?

Development of the .223 Rem. began in 1957, an effort in concert with Eugene Stoner as he downsized his original AR-10 to become what the U.S. government requested—a .22-caliber that would ultimately begin service in Vietnam as the M-16. It chambered the new cartridge and the combination was quickly adopted by the military.

In 1964 Remington submitted the new ammunition design to SAAMI for commercial standardization—a process that includes establishment of pressure limits, physical size, chamber dimensions and more. Civilians had their first chance to shoot it that year.

Supplying U.S. troops with one type of ammunition, while NATO allies fielded others, was a logistical nightmare. With that in mind, FN set about creating a shared cartridge that could run reliably in machine guns, short-barreled carbines and most other firearms issued by those countries facing the growing communist threat. That required subtle modification, increased pressure and the slight chamber reshaping. Almost two decades NATO adopted it and what began as a .223 Rem. became 5.56 NATO, also often referred to as 5.56x45 mm.


What's the Difference?

Pressure Levels

They look virtually identical, but the difference between .223 Remington and 5.56 NATO is a significant one. To start, 5.56 generates Sporting Arms and Ammunition Manufacturers’ Institute (SAAMI) standardized pressure levels of roughly 58,000 psi, while 223 tops out at around 55,000.

223 in a 223 Wylde Chamber


Throat Length

That may not seem statistically huge, but it’s increased by unseen differences in the firearms and ammunition. The throat in a 5.56 NATO-chambered gun is longer by .125 inch, for example. That space allows military firearms to run reliably through heavy volumes of fire between cleanings, but it also bleeds a slight bit of pressure before the bullet fully engages the rifling’s lands and grooves. To compensate, and take advantage of space available, another grain or so of powder is added to the case.



A .223 Rem. chamber, on the other hand, engages the cartridge and bullet more snugly, capturing the maximum amount of energy possible. As Hornady Ammunition warns on its law enforcement website, you can expect “…a .223 chambered weapon to run at approximately 65,000 psi or more” if you run a 5.56 NATO cartridge through it. That’s a serious pressure increase with dangerous implications.

Owners of a a 5.56 NATO-chambered firearm, on the other hand, can safely use .223 Rem. cartridges. The reverse is not true, however. Injuries or worse from that mismatch may be rare, but owners of .223 Rem. rifles or handguns must use that ammunition, exclusively.



The two cartridges are virtually identical in appearance, and at the range only distinguishable by headstamp. It’s for that reason—and others explained later—manufacturers like Bear Creek Arsenal don’t offer .223 Rem.-chambered AR-15s or AR-15 uppers. Those chambered in 5.56 NATO are more versatile and run a wider selection of loads.



ARs siphon a portion of the gas released when a cartridge is touched off to move the bolt carrier group rearward, extracting the spent brass and ejecting it. The buffer spring, compressed during that cycle, pushes it back forward, picks up a fresh cartridge during that travel and finally returns the gun to full battery, ready for the next shot.

It’s simple in principle, but the delicate balancing act relies on tapping the right amount of pressure to set the parts in motion, at the right velocity. It’s rare, but that slight drop in .223 Rem. ammunition’s pressure may fall short of the requirement when it’s run in a 5.56 NATO AR-15. The frustration is rare and usually limited to extreme changes in bullet weight. A few experiments with different loads almost always remedies the frustration, and adjustable gas blocks are another solution.

5.56 AR-15 Shooting at Target


Performance & Accuracy

About the only disadvantage to running .223 Rem. ammo in a 5.56 NATO-chambered gun is a slight loss in performance. It’s a byproduct of that minute, but ballistically significant, extra space before the bullet fully engages the rifling. That results in a modest sacrifice in pressure, a proportionate loss in muzzle velocity and that momentary instability can compromise accuracy slightly.

Groups may widen at 100 yards, although witnessing the difference takes practiced hands, a steady rest and wind calm enough that mirage is boiling. The loss in precision is undetectable to most enthusiasts, particularly at AR-15 distance, even when they’re lucky enough to encounter ideal conditions. Skill, bullet weight, rifling and maintenance play bigger roles.

223/556 Ammo Selection


Ammo Selection

Obviously, 5.56 NATO rounds are best in a 5.56 NATO chambered gun, but the ability to run either cartridge in a single gun is a decided advantage for hunters who pursue anything from varmints to predators and big game (where regulations allow the use of a .22-caliber centerfire, of course).

Hornady offers one of most diverse selection of loads available today, but even it offers 5.56 NATO in only four different bullet weights—55-, 62-, 68- and 75-grains. The projectiles are, however, available in a wide variety of styles.

In .223 Rem., though, you can choose between 35-, 50-, 53-, 55-, 62-, 68-, 73- and 75-grains brass 223 ammo. And you can select polymer-tipped designs for varmints, match grade, FMJs and more. As mentioned above, going too heavy or light in the projective can compromise the semi-auto’s reliability, so run a box or two before opening day.


Added Versatility

Bullet diameter in the 5.56 NATO and .223 Rem. cartridges is identical—0.224 inch. That means muzzle devices and suppressors are 100-percent compatible. Thanks to the cartridges being nearly identical physically—with the headstamps being the only readily identified exception—the magazines are as well.

Perhaps the biggest advantage to 5.56 or 223 Wylde, though, is the increased availability of ammunition. When supply lines strain to 2020 levels the odds are still good you’ll find military-style loads and even some surplus at your favorite FFLs or even gun shows. If not, they’re almost guaranteed to be the first to make it back onto the shelves.

223 Wylde with Ammo


223 Wylde: The Perfect Compromise?

The .223 Wylde chambering is the relatively modern invention of Bill Wylde. It’s not a cartridge, but a compromise design that allows the safe use of both 5.56 NATO and .223 Rem. ammunition in the same gun.

The key difference is the fact that .223 Rem. bullets aren’t required to travel as far as they do in a 5.56 NATO chamber before encountering rifling. Shortening that distance preserves more of the round’s accuracy potential.

It is, however, far enough that 5.56 cartridges remain at safe pressures during operation. It’s a solid design, but a compromise. It doesn’t quite attain the full potential of either cartridge, although it has gained favor in some competitive shooters. [Check out our selection of 223 Wylde uppers and 223 Wylde barrels and read more about 223 Wylde in our complete guide!]

Shop 223 Wylde Uppers


Which is Better?

[In most instances, you'll likely want a 5.56 or 223 Wylde chambered AR-15 over a .223 Remington specific AR. Shooting a 556 or 223 Wylde AR15 allows you to double your ammo selection, which can not only allow you to choose exactly what you want for plinking, target shooting, or hunting, but can also save you time and money when finding ammo as we've seen in the 2020 and 2021 Ammo Shortage.]5.56 NATO is the most popular on the market today, and for good reason. It’s built on decades of military experience and civilian testing and more modern shooters are taking advantage of that refinement than ever before.

It is, after all, America’s favorite firearm. [Be sure to check out our other helpful guides such as AR10 vs AR15 and 308 vs 556 and leave a comment with your thoughts on this topic!]

Shop 556 Uppers


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mike meadors
August 29, 2021
This was a great read. It was really informative. And I appreciate that they added the info about .223Wylde as well. Ive often wondered about that round, but never inquired about it. Thanks for the education. It's important that people in this hobby/lifestyle continue to educate themselves on the items we love so much. There's nothing more irritating than hearing a (usually new) shooter quoting bad and often dangerous information. Not as a fault of theirs, but just because they didn't educate themselves. They likely heard it or overheard it from another uneducated noob or just an uninformed individual. Keep educating yourselves people. No one will learn it for you.
September 5, 2021
First time buyer of an ar15 I'm impressed with the way it shoots and the way it handles. Bought it from Bearcreek. Thanks
September 7, 2021
Awesome. I have learned something new and got my confusion cleared. Thanks
September 16, 2021
Great information comparing the 223 wylde vs the .556 this should show the new shooters how to make a better choice.
Aaron Short
December 4, 2021
Honestly I expected more out of a 223/556 as in I would think that in all these years of either cartridge. they would have came up with a larger more ballistically sound bullet, staying in the same size (223/556) but performing more ballistically sound at longer ranges, without sacrificing ballistic coefficients. as compared to it larger cousin the 308 In other words heavier bullet, longer ranges, less bullet drop while maintaining the same or better fps. out of a 223/556 out to 600 meters, almost doubling it effective range of 460 meters. I hope you get what I am trying to say, because I don't know if I am explaining that right. I just expected more innovation out of the 223/556. I still love it. and always will. I just expected more out of it in these decades of its existence. as so to compete better with the larger grain bullets such as the 7.62x39
November 22, 2022
They did. First M193, then M855, then M855A1.
November 22, 2022
By reading the comments above, seems like they're more confused than ever
November 22, 2022
Very good informative article comparing the 2 cartridges. Keep up the good job by posting more article's like this one. Thanks !
Keith Wyrick
January 3, 2023
Very helpful article, thanks for the education!
Scott wood
January 3, 2023
Great article, I wish they had gone a little more into the 223 wilde chambering though. What exactly is the difference between the 5.56x45, the 223 Remington, and the 223 wilde chambering? I know it’s the compromise between the two originals but is there a way to maximize the use of your 223 wilde. A different throat size?
January 3, 2023
John Chermak
January 12, 2023
Thanks that was a very good explanation of the difference between the two similar types of ammo and the firearms that use them.
Mike Garrett
February 19, 2024
What about reloading the two? After sizing, is there still a difference? Same load,same size.
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