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5.56 NATO vs .223 Remington vs .223 Wylde

5.56 NATO vs .223 Remington vs .223 Wylde

Posted by 80-Lower.com on Nov 17th 2020

There's one question every new AR owner asks when they buy those first boxes of ammo: Can you shoot 5.56 NATO in a .223 Remington gun? What is .223 Wylde, anyway? How does it all compare? We're explaining everything about the AR-15's most popular cartridges. Let's go.


.223 Remington Came First

The .223 Remington cartridge saw development in 1957, directly linked to the development of the AR-15. The military wanted to ditch the .30-caliber round used in WWII and then in service in the M14. Top brass had their requirements for the new round's performance. It had to:

  • Be .22 caliber to reduce size and weight.
  • Have a magazine capacity of 20 rounds.
  • Exceed supersonic speeds at 500 yards.
  • Penetrate .135" of steel plate at 500 yards.
  • Be as accurate as M2 ball (.30-06) ammo.
  • Be chambered in a weapon system weighing no more than six pounds.
  • Be able to penetrate a steel helmet at 500 yards. Keep this in mind for later.

To meet these requirements, engineers figured out the bullet needed to weigh 55 grains and travel around 3,300 feet per second. Those engineers settled on using the .222 Remington (not a typo) as a test bed, a popular varmint hunting round introduced in 1950. They made the cartridge longer and faster, and .223 Remington was born.

In 1964, the Armalite Rifle's design was adopted by the U.S. Military, and the M16 automatic rifle was distributed to troops just in time for Vietnam. Along with it came the final design and circulation of the updated Remington cartridge. End of story, until 1980.


5.56 NATO Was Made For More Power

Unfortunately, .223 Remington did  not do a great job at penetrating steel at distance. It also had some reliability issues in Vietnam. To make .223 more reliable and deadlier at range, service requirements were beefed up. The round now had to penetrate a steel helmet at 800 yards, the same as the larger 7.62x51 NATO. 

To accomplish this, new cartridge dimensions and internal chamber pressures were drafted onto the .223 Remington. The round was reshaped with a better drag coefficient. It had more muzzle energy and higher velocity. Even more powder was added to make the magic happen. The brass had to be just slightly thickened to handle the added pressure. Finally, the chamber itself had to be redesigned to accommodate the new brass and pressure, and 5.56 NATO came to be.


.223 Rem and 5.56 NATO Compared

Specifications and Pressure

  • 5.56 NATO uses a higher internal chamber pressure of 62,000 PSI.
  • .223 Remington maxes out chamber pressure at about 55,000 PSI. 

Shooting a 5.56 NATO cartridge out of an AR-15 with a .223 chamber will result in a greater pressure than the chamber is designed for. This over-pressurization is why many shooters say it's not safe to shoot 5.56 in a .223 gun. But this only tells half the story. It's not just more powder in the cartridge causing the higher chamber pressure with 5.56 loads in .223 guns.

Chamber Differences

The real difference between 5.56 and .223 isn't the cartridges, but the chambers and barrels of the guns firing these two cartridges. Remember those reliability issues the M16 suffered in Vietnam? When the rifle got dirty and gunked up, tight tolerances made chambering rounds and cycling the weapon difficult. The Army also wanted a more powerful round that could better penetrate light steel and enemy combat helmets. To address reliability concerns and to "juice up" the .223 Remington for battle, engineers redesigned the M16's chamber. They made the leade of the chamber slightly larger, so it wouldn't bind up in battlefield conditions. The larger chamber also allowed for more pressure to build safely, increasing velocity and penetration at distance. 

Why The Barrel's Leade Matters

The leade is the throat, or opening of the chamber just before the rifling. It's where pressure builds and forces the round down the barrel.  The 5.56 chamber's longer, wider leade allows for longer bullets, higher pressure, and more reliability in the field when things get dirty. 

The .223 chamber's shorter, thinner leade allows for tighter tolerances, optimal velocity, and better accuracy with less powder and lower pressure. This is where the possible danger of chambering 5.56 in a .223 gun comes out. Shoving 5.56 NATO into the smaller leade of the .223 chamber could cause pressures to build higher than they would if only the added powder was a factor. Some believe this aggregate pressure could spike, possibly damaging your rifle or even harming you.

So, is 5.56 safe in a .223 gun?

Shooting 5.56 NATO in a .223 Remington AR-15 or other rifle is generally safe and will probably not result in a catastrophic failure, but it is not recommended. This inhibits accuracy and over time, your rifle will early show signs of barrel wear and throat erosion.

To verify the safety aspect of this question, one AR-15 owner named Andrew spent months conducting tests. He shot 5.56 rounds in a .223 AR-15. After firing various cartridges and recording their pressures, he came to an anti-climactic observation: The Remington rifle's chamber over-pressurized by just 10% beyond its rated 55,000 PSI. That means with the shorter leade and differences in cartridges, the 5.56 rounds still only reached their advertised 62,000 PSI in the .223 chamber. 

This difference is well below the pressure created by high-pressure proof rounds manufacturers use to test a new barrel. In fact, this "over-pressurization" is technically within safe operating ranges of the .223 Remington AR's chamber and barrel. Regardless of the cartridge, AR-15 barrels and chambers are forged in the same machines, from the same metals, with the same heat treatments and coatings, and generally the same thickness.

Can I shoot .223 in a 5.56 gun?

Shooting .223 Remington in a 5.56 NATO gun is perfectly safe. Doing so will not result in damage, early throat erosion, or barrel wear. Accuracy will be slightly diminished at distance. This is because the lower pressure of the Remington cartridge combined with the larger dimensions of the 5.56 chamber creates sub-optimal velocities and bullet stability in flight.


What is .223 Wylde?

Even though shooting 5.56 in a .223 gun is safe, you should avoid it if you can. After all, you don't want to burn your new black rifle out early. Trying to remove that barrel nut after it's been torqued, heated, and cooled for a few months at the range is nearly impossible. Recoil may feel worse. Accuracy can also suffer and what's the point of an inaccurate black rifle? But ammo shortages happen, and prices get weird. Sometimes you may only have access to one cartridge or the other. Given how similar these rounds are, you should have the ability to shoot either one without worrying about ruining your rifle.

That's where .223 Wylde comes in. Wylde is not a third cartridge alongside Remington and NATO. Instead, it's a hybrid rifle chamber made to handle both NATO and Remington rounds safely and accurately. 

How does it work?

The .223 Wylde chamber provides a simple compromise in dimensions and the barrel's leade. It's a perfect "in-between" option that allows 5.56 NATO and .223 Remington to safely and accurately meet in the middle, in one gun.

Is there any downside?

Besides cost? No. Of course, it's perfectly understandable that many rifle owners -- especially AR-15 owners -- prefer running entirely mil-spec components. In this case, there is nothing wrong with sticking to a 5.56 NATO chamber. Remember, it can safely fire .223 Remington.

Why invest in a Wylde chamber?

Why not? The 5.56 NATO cartridge is a workhorse, made not for extreme accuracy but for combat and high volumes of fire. Buying 5.56 gun means you get to enjoy cheap ammo, but you lose out on accuracy when you load Remington in the NATO chamber. The .223 Remington cartridge is made for accuracy, with tons of special and match-grade ammo available. If you get a Wylde chamber, that means you get to maximize performance and edge out even the best military-issued rifles. But when you get tired of spending $1.00 to $1.50 per round on those Match King tack-drivers, you can simply go back to buying $0.30 to $0.50 NATO rounds.

How well does Wylde work?

We've got more data from the fine folks at www.ammunitiontogo.com. They collected muzzle velocity data by firing 5.56 NATO from a Colt LE9620, and a Pro Firearms 223 Wylde rifle. Both rifles were fitted with 16" barrels and the same gas systems. So, did the Wylde chamber allow NATO rounds to maintain proper (safe) pressures?

55-Grain (M193) Ammo Results

This guide covers M193 and M855 NATO rounds.

223 Wylde Muzzle Velocity:

  • Trial #1: 3,013 FPS
  • Trial #2: 3,011 FPS
  • Trial #3: 3,039 FPS
  • Trial #4: 3,046 FPS
  • Trial #5: 3,031 FPS
  • Average: 3,031 FPS

5.56 NATO Muzzle Velocity: 

  • Trial #1: 3,033 FPS
  • Trial #2: 2,973 FPS
  • Trial #3: 2,996 FPS
  • Trial #4: 2,999 FPS
  • Trial #5: 2,996 FPS
  • Average: 2,999 FPS

Comparing averages, we get a 1% difference in muzzle velocity between the two chambers. The graph above shows amazing consistently between each trial run, too. This indicates with no doubt that chamber pressures are just about exact in both guns. The result is a gun that can safely and accurately chamber both 5.56 NATO and .223 Remington, without sacrificing the performance of either.

What about the Wylde barrel itself?

The barrel on any .223 Wylde is no different in construction, rifling, or performance than any other .223 Remington or 5.56 NATO barrel. They use the same alloys, coatings, treatments, gas systems, and twist rates. Only the chamber itself differs slightly between these three sets of specifications.

Is Wylde compatible with all AR-15 parts?

Yes. Beyond tiny measurements, the .223 Wylde chamber is indiscernible from any other .223 Remington or 5.56 NATO chamber. No special parts or modifications are required if you want to install a Wylde barrel on your current .223/5.56 rifle. Barrel nuts, receivers, lower parts, gas system parts, the bolt and carrier, buffers, springs, magazines, and everything else remain the same.

Is there 5.56 or .223 the Wylde can't shoot?

No. If any 5.56 NATO or .223 Remington round is being advertised as such, then the Wylde chamber can safely shoot it. That's why investing in this chamber is so great: You get access to every type of commercial and mil-spec .22-cal AR cartridge on the market, minus any risk or hit to performance.


Quick Recap

We covered alot of info today, so here are the most important takeaways:

  • 5.56 NATO operates at a higher pressure than .223 Remington.
  • Testing has shown 5.56 is generally safe to shoot in a .223 gun.
  • When tested, 5.56 did not exceed normal pressure in a 223 gun.
  • Shooting 5.56 in a .223 gun will, over time, still cause early wear.

Most of all, consider the .223 Wylde chamber if you're dead-set on regularly cross-loading these two rounds in a single rifle. Given how similar both cartridges are, it makes sense to invest in the Wylde chamber if you're willing to spend a few extra bucks. You'll improve barrel life, reduce carbon fouling when shooting NATO, and you'll get overall higher accuracy than with the other two "dedicated" chambers.

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