5.56 vs .223: What’s the Real Difference?

Last updated and checked November 8, 2026 · By Nick Hall, AR-15 shooter who has run both 5.56 NATO and .223 Remington loads through the same rifles

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Quick Answer: In 5.56 vs .223, start with the barrel stamp. Never fire 5.56 NATO in a barrel marked only .223 Remington, because SAAMI calls that an unsafe combination. SAAMI clears .223 Remington in a 5.56 military-spec chamber, and makers build .223 Wylde chambers to take both, which is why Wylde is what I’d buy for almost every new AR-15 build in 2026.

.223 Remington is the civilian cartridge, rated at 55,000 psi by SAAMI, and the longer throat in a 5.56 NATO chamber costs it a little accuracy. 5.56 NATO is the military cartridge, rated at 62,366 psi under NATO’s EPVAT, and since those two numbers come from different test systems you shouldn’t read them as one clean gap. .223 Wylde pairs a 5.56-style leade with a tighter .224-inch throat.

Check the barrel marking before loading. If it says “.223 Rem” only, run only .223 Remington ammo. If it says “5.56 NATO” or “.223 Wylde”, it’s meant to take both, and your manual or the maker has the final word. Modern factory ARs almost always ship with .223 Wylde or 5.56 NATO chambers.

Table of Contents

If you’ve spent more than five minutes in the AR-15 world, you’ve heard the .223 vs 5.56 question: can I shoot 5.56 in my .223 chamber? It matters more than most people think, because getting it wrong can damage your rifle or, worse, hurt you.

I’ve seen cracked bolt lugs and blown primers from guys who didn’t understand the difference. These two cartridges look identical on the outside, but the pressure specs and chamber dimensions tell a very different story.

Also see our head-to-head comparison: .223 vs .308.

The Short Answer

You can safely shoot .223 Remington in a 5.56 military-spec chamber. You cannot safely shoot 5.56 NATO in a .223 Remington chamber. And .223 Wylde is built to handle both, with the barrel maker as the authority. The 5.56 vs .223 difference comes down to chamber specs and pressure ratings.

Most modern AR-15 rifles are chambered in 5.56 NATO or .223 Wylde, so the odds are on your side. But odds aren’t a barrel stamp. If you own an older bolt-action or a varmint rifle stamped “.223 Rem” only, pay attention. This could save your rifle and your face.

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5.56 vs .223 Chamber Pressure: The Core Difference

Almost every 5.56 NATO vs .223 Remington article you’ll read says the 5.56 runs about 13% more chamber pressure. For years that comparison was shaky, because it set a SAAMI number beside a military number. On October 12, 2026, SAAMI changed the picture.

SAAMI, the civilian standards body, rates .223 Remington at 55,000 psi maximum average pressure, measured with a conformal piezoelectric transducer. You’ll find that figure in ANSI/SAAMI Z299.4, the centerfire rifle standard.

SAAMI has now accepted a new cartridge called 5.56 Commercial, or 5.56 COMM, introduced by Hornady, at 62,000 psi. It’s measured with the same transducer procedures as .223 Remington, so for the first time you can set 55,000 psi beside 62,000 psi from one standards body, and the gap of about 13% is real. SAAMI’s 5.56 Commercial notice is three pages, and it’s worth reading.

One catch: 5.56 COMM is not 5.56 NATO. SAAMI says conformance “does not imply or ensure conformance with any military or NATO specification,” and that no public standard exists for 5.56 NATO. So 62,000 psi is the number for 5.56 COMM, and the numbers for 5.56 NATO still depend on who measured it: the US Army’s SCATP 5.56 procedure rates it at 380.00 MPa, which is 55,114 psi, while NATO’s EPVAT puts it at 62,366 psi.

CIP, the European authority, rates .223 Remington at 430.00 MPa, 62,366 psi, the same figure NATO publishes for 5.56. That’s why you should never compare a number from one system with a number from another, and why the old quote of 55,000 against 62,366 psi was never a clean comparison.

What SAAMI did not change is the safety rule. In its words, “the use of any 5.56 ammunition, including all military variants as well as ammunition produced to this standard in a 223 Remington chamber creates increased pressure and is considered an unsafe combination.”

I’ve personally chronographed M855 5.56 ammo running about 50-100 FPS hotter than equivalent .223 loads from the same barrel length. That’s by design, because NATO wanted reliable cycling in full-auto platforms under adverse conditions.

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Chamber Dimensions: The Leade Matters

The chamber matters as much as the pressure figure. A 5.56 NATO chamber has a longer throat, the stretch between the case mouth and where the rifling begins: a straight section called freebore, then the tapered leade. That extra space gives the bullet room to accelerate before it engages the rifling, which keeps pressures manageable.

A .223 Remington chamber has a shorter, tighter leade, and it’s designed for accuracy, not for handling hot military ammo. Stuff a 5.56 round into that tighter space and the bullet hits the rifling sooner.

Think of it like a highway on-ramp. A longer ramp, the 5.56 chamber, lets the bullet merge smoothly. A short ramp, the .223 chamber, forces everything to happen too fast, and pressure spikes are the result.

The same round will produce a higher peak in the tighter chamber, because the load stays the same while the room the bullet has before it hits the rifling shrinks. A 5.56 round seated with a long ogive can be touching the lands before the bolt has finished locking, and the pressure has to go somewhere.

SAAMI’s 5.56 COMM drawing shows the difference: a .2262-inch throat and a 1 degree 13 minute leade, against the .224-inch throat and 3 degree 10 minute leade on the .223 Remington drawing in Z299.4.

Be careful with leade numbers you see quoted online. SAAMI publishes a full cartridge and chamber drawing for .223 Remington, and now for 5.56 COMM. There is still no public drawing for 5.56 NATO, so the leade figures that circulate online come from military prints and from people measuring real barrels. Treat any exact decimal you see for a 5.56 NATO leade as a good working figure rather than a published spec.

Is Headspace Different Between .223 and 5.56?

No, and that surprises people. SAAMI’s .223 Remington chamber headspaces at 1.4636 to 1.4736 inches, and its new 5.56 COMM chamber at 1.4636 to 1.4730. Both cartridges are drawn at the same 1.4666-inch maximum. The difference is forward of the case: a .224-inch throat with a steep leade in the .223, and a .2262-inch throat with a long, gentle leade in the 5.56 COMM.

That’s why the same go gauge checks both, and why it can’t tell you which chamber you have. There’s still no public drawing for 5.56 NATO, so I’m not going to print military headspace decimals here.

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5.56 vs .223 Comparison Table

This is 5.56 NATO vs .223 Remington by the numbers, so read each row across, and don’t compare a number in one pressure row with a number in another.

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Can You Shoot 5.56 in a .223 Chamber?

No. And I don’t care what your buddy at the range says. SAAMI calls it unsafe and warns it can cause serious injury or death. Chamber pressure in that tight .223 throat can land barely over spec with one load and top 70,000 psi with another, and you won’t know which you’ve got.

Will it blow up every time? Probably not. But “probably not” isn’t a standard I’m comfortable with when a chamber is inches from my face.

The warning signs include flattened or cratered primers, difficult extraction, brass showing pressure signs at the case head, and in serious cases, cracked bolt lugs. I’ve seen a Remington 700 in .223 that a guy had been feeding M855 through. The bolt lugs had visible stress cracks after about 500 rounds. That rifle was done.

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Can You Shoot .223 in a 5.56 Chamber?

Yes, in a chamber built to 5.56 military spec, which is what SAAMI’s FAQ covers. SAAMI also warns that plenty of non-military 5.56 chambers are out there, so unless you know yours is mil-spec, check the manual or ask the maker, because a 5.56 stamp alone won’t tell you.

You’re running lower-pressure ammo in a chamber designed for higher pressure. The only downside is a small accuracy loss, because that longer leade in the 5.56 chamber gives the bullet more room to yaw before it engages the rifling.

In practice, I’ve shot plenty of match-grade .223 through 5.56 barrels and gotten acceptable accuracy. We’re talking maybe 0.25-0.5 MOA difference at 100 yards, which 99% of shooters will never notice. If you’re a benchrest competitor, sure, it matters. For everyone else, it’s a non-issue.

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What SAAMI’s New 5.56 COMM Changes

Today, not much for your rifle, because the barrel-stamp guidance hasn’t moved and nobody we track sells 5.56 COMM yet.

SAAMI issued the 5.56 COMM drawings in June 2026 and announced the standard on October 12, 2026. Before that, the only SAAMI chamber in this family was .223 Remington, last revised in 2023. Put the two drawings side by side and you get the comparison nobody could make before: one standards body, one test method, two chambers.

Your rifle’s marking still decides. Marking a gun or a case 5.56 COMM is voluntary, so nothing about your barrel stamp changed, and a barrel marked only .223 Remington still takes only .223 Remington.

Don’t assume 5.56 COMM and 5.56 NATO are interchangeable. SAAMI says the lack of a public 5.56 NATO standard makes blanket compatibility statements “impossible.” If you buy 5.56 COMM ammo, and your rifle isn’t marked for it, ask the maker of the rifle or the ammo first. The same goes for .223 Wylde, which is a maker’s spec and not a SAAMI one.

You can’t buy it yet. None of the retailers we track list 5.56 COMM ammo or rifles as of November 8, 2026. When they do, I’ll update this page. Until then, we’ve got more on what SAAMI’s 5.56 Commercial standard means.

.223 Wylde vs 5.56 NATO: The Best of Both Worlds

Wylde settles this whole debate, and it’s what I recommend for most AR-15 builds. Bill Wylde of Greenup, Illinois drew it up to get match accuracy out of 5.56 rifles in NRA High Power competition. It’s a hybrid chamber built to handle 5.56 NATO pressures safely while holding on to most of the accuracy of a .223 Rem chamber.

Wylde pairs a 5.56-style leade angle and length with the .224-inch freebore diameter of .223, so you get safe 5.56 feeding with match-grade accuracy potential. The one downside is that it’s a maker’s spec and not a SAAMI one, so the barrel maker’s word is what counts, and that includes 5.56 COMM. Most of the best AR-15 barrel makers, including Criterion, Faxon and Ballistic Advantage, offer .223 Wylde as a standard option.

If you’re building a new rifle and weighing .223 Wylde vs 5.56 NATO, go with .223 Wylde. I’ve been running Wylde chambers on my precision AR builds for years and the accuracy with both .223 match ammo and 5.56 ball has been very good. Check out our best AR-15 rifles roundup for top picks that come chambered in Wylde.

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Why One Is Called .223 and the Other 5.56

This trips people up constantly, and the SAAMI drawing clears it up: the 5.56 is the barrel’s bore in millimeters, and .223 is just a name that sits close to the groove figure.

SAAMI specifies the .223 Remington barrel as .219 inch bore diameter, which is 5.56 mm, and .224 inch groove diameter, which is 5.69 mm. Bore is the hole before the rifling grooves are cut. Groove diameter is what the bullet actually has to fill, and the bullet itself is .2245 inch.

So the metric name comes from the bore, the .223 matches neither figure, and neither one is the bullet diameter. If the naming had been consistent we’d be calling it 5.69, or .224, and nobody would ask this question.

And the x45 in 5.56x45mm? That’s just the case length in millimeters.

So is 5.56 bigger than .223? No. SAAMI draws the bullet at .2245 inch on both its .223 Remington and 5.56 COMM drawings, and the cases share the same outside shape. What differs is the pressure and the chamber, not the size of the round.

The Twist Rate Nobody Checks

Buying an older .223 rifle for heavy bullets? This one catches people. SAAMI’s reference twist for .223 Remington is 1 in 12, while military 5.56 barrels run 1 in 7, and most modern AR-15s are 1 in 7 or 1 in 8. SAAMI’s 5.56 COMM drawing lists 1 in 7 too.

That difference decides which bullets you can actually shoot. A 1 in 12 barrel will stabilize 55 grain ball fine and will keyhole 77 grain match bullets at distance. You won’t hurt the rifle, but you can’t fix it short of a new barrel, so check the twist stamp before you buy heavy ammo for an older varmint rifle. I’ve watched a guy burn through a box of 77 grain trying to work out why his groups looked like buckshot.

Military vs Civilian Specs

The .223 Remington came first. The military adopted it for the M16 as the M193, and NATO built the 5.56 NATO cartridge on it later, around FN Herstal’s 62 grain SS109, and standardized it under STANAG 4172 in October 1980. Common 55 grain M193 ball and 62 grain M855 are the two military loads you’ll see most. Military ammo has to function in full-auto weapons, in extreme temperatures, after being stored for decades, and in dirty conditions, and that’s why the specs are hotter and the chamber is more forgiving.

The .223 Remington is the civilian SAAMI-spec round, and Remington introduced it commercially in 1964, right around the time the military adopted the M16. The civilian version has lower pressure limits because SAAMI builds in larger safety margins for the wide variety of firearms that might chamber it.

Commercial ammo labeled “.223 Remington” from Federal, Hornady, or similar is loaded to SAAMI specs, and ammo labeled “5.56 NATO” or “5.56x45mm” is loaded to NATO specs. Some manufacturers, like Black Hills, produce both versions and clearly label them.

If you want the military-style 55 grain load itself, M193 is what to look for on the box. It’s the plinking round most 5.56 rifles were built around.

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5.56 vs .223 Ballistics: Velocity, Energy and Drop

In 5.56 vs .223 ballistics, the gap is small with the same 55 grain bullet. Winchester’s two FMJ loads sit just 30 fps apart in muzzle velocity, and the drop figures below are from a 100-yard zero. Winchester’s figures don’t name a test barrel, so treat them as a side-by-side of two loads, not a rule.

You won’t feel that at the range, and recoil is a tie in practice. Most 5.56 loads run about 5 to 6 ft-lb.

Barrel length moves these numbers more than the label does. PMC publishes its own data by barrel: its Bronze .223 runs 2,900 fps from a 16-inch barrel and 3,200 from a 24-inch, and its X-Tac 5.56 runs 3,120 fps from 16 inches and 3,270 from 20.

SAAMI’s 5.56 COMM reference load is a 55 grain bullet at 3,400 fps from a 20-inch test barrel, against the 24-inch barrel SAAMI uses for .223 Remington, so don’t set it beside the Winchester figures. Nobody we track sells it yet.

Which Is Better for Hunting and Home Defense?

Neither label wins on its own, because terminal performance comes down to the bullet more than the headstamp. The 55 grain FMJ on the cards below is a range load, so for hunting pick an expanding load built for the job, and check your state’s hunting rules on the caliber before you take it to the woods. For a house gun, see our AR-15 home defense setup guide.

Accuracy Differences

In terms of inherent accuracy, .223 Remington match ammo in a .223 chamber will outperform 5.56 ball ammo in a 5.56 chamber.

But that’s comparing match ammo to military ball, which isn’t really fair, and the chamber has less to do with it than the ammo quality.

Match-grade 5.56 ammo like Mk 262 or Black Hills 77gr OTM shot from a quality 5.56 or Wylde barrel shoots very tight. Sub-MOA is very achievable, and the chamber specification matters far less than barrel quality, ammo consistency, and the person behind the trigger.

For the best accuracy with the widest ammo compatibility, a .223 Wylde barrel with a 1:8 twist rate is hard to beat. That combination handles 55gr plinking ammo and 77gr match loads, and it does both well.

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Barrel Markings: How to Tell What You Have

Check your barrel. Seriously, go look right now. The chamber specification should be stamped or engraved on the barrel, near the chamber end.

You’ll see “5.56 NATO,” “.223 REM,” “.223 WYLDE,” or possibly “5.56/223.” Some older or cheaper barrels may only say “.223” without specifying further, and if yours does, call the maker before you fire it and keep 5.56 out of it until you hear back. On a free-float AR, the stamp may be hidden under the handguard, so the receiver markings don’t settle it.

Can’t find a marking? Check the manufacturer’s documentation. If you bought it new, it’s in the manual, and if you bought it used with no paperwork, contact the manufacturer with the serial number. Don’t guess on this one.

Nearly every AR-15 sold in the last 20 years is chambered in 5.56 NATO or .223 Wylde. The .223-only chambers are mostly found on bolt-action rifles, older Ruger Mini-14s, and some single-shot rifles, but verify before you load that first round. For more on barrel specifications, see our AR-15 barrel length guide.

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What About Reloaders?

If you reload your own ammo, this distinction matters even more, and our guide on how to reload .223 and 5.56 covers it. 5.56 NATO brass tends to have thicker case walls and less internal volume than .223 brass, so if you use load data developed for .223 brass and apply it to 5.56 brass without reducing the charge, you can get pressure spikes.

Always sort your brass by headstamp. Keep military brass, meaning LC, WCC and FC with the NATO cross, separate from commercial .223 brass. Work up loads separately for each. This is basic reloading safety, but I’m amazed how many people skip it.

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My Recommendation

For any new AR-15 purchase or build, go with .223 Wylde. It’s built to take .223 Remington and 5.56 NATO safely, and it shoots both well. Already own a 5.56 NATO rifle? You’re good to shoot 5.56 NATO and, in a military-spec chamber, .223 Remington, and your manual or the maker can confirm the chamber. 5.56 COMM is a separate question for that same maker. If you own a rifle stamped .223 only, stick to .223 Remington ammo and don’t take chances.

My AR-15 ammo guide covers specific loads for both chamberings, and if you’re still figuring out your ideal AR-15 caliber, our caliber guide goes deep on every option available for the platform. Weighing .300 Blackout instead? Our .300 Blackout vs 5.56 comparison covers that one.

Don’t pay extra for either label, either. PMC makes a clean comparison, because it sells the same 55 grain weight under both labels. Today, PMC X-Tac 5.56 starts at $9.49 and PMC Bronze .223 at $9.66 for 20 rounds, so you pay 47 to 48 cents a round either way.

You’ll find a far bigger choice of .223 loads on the shelf, which is one more reason a Wylde barrel earns its keep. Don’t overthink .223 vs 5.56. Check your barrel marking, buy the right ammo, and go shoot.

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