.223 vs. 5.56: What's the Difference

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.223 vs. 5.56: What's the Difference

Most people who are new to the world of firearms don’t know the difference between .223 Remington and 5.56 NATO ammo. In fact, many people wrongly assume that these two kinds of ammo are interchangeable. This is false, though! Using these ammos interchangeably can actually be extremely dangerous. 

.223 and 5.56mm ammo are used in AR-15 rifles. One difference between them is the round itself. The 5.56mm ammo is slightly hotter than the .223. Also, the powder charge, projectile, and rifle specifications between the two are different. Always check what your AR-15 is chambered for since these details will vary from gun to gun. 

Differences between the two may appear minor, but they can have a huge impact on performance. To safely operate a rifle, you must use the specific ammo that it is chambered for. Under no circumstances should you disobey this rule. 

In this article, we will be reviewing the contrasts between .223 Remington and 5.56 NATO ammo, going over the nuanced differences between the two. Before using your AR-15, it is imperative to learn about its structure and how it works. Being informed on how to use it will pay off greatly when it’s time to actually do so. 

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Case and Leade Size

One of the main differences between .223 and 5.56mm ammo is the size of their leades, or freebores. The leade is the distance between the mouth of the case and the point at which rifling starts in the barrel. 

The two ammo cases are identical in size, but the leade of 5.56mm ammo is longer and rounder than the .223mm ammo. In effect, this creates a wider, farther-reaching space for the bullet to travel through before hitting the grooves of the barrel, and thus, a more powerful shot. 

This tightly sealed projectile of the .223 Remington chamber produces more pressure and a hotter powder charge than the 5.56 NATO chamber due to more gas being released through the larger leade. 

This longer throat also allows for about one more grain of powder to be loaded into a 5.56 NATO cartridge than the .223 Remington. This extra capacity is what makes the 5.56 NATO so powerful.


Another major difference between these two types of ammunition is the higher pressure level of the 5.56 NATO cartridge than the .223 Remington. The 5.56 NATO cartridge runs at approximately 58,000 psi, while the 223 Remington is loaded to approximately 55,000 psi.

Because of these differences, firing a .223 round through a 5.56mm chamber will cause lower pressure than what is expected for the firearm, which is very unsafe. Vice versa, firing a 5.56mm round through a .223 chamber will cause higher pressure than what is expected, which is also unsafe. 

Running a 5.56 NATO cartridge in a rifle chambered for a .223 Remington cartridge will cause the weapon to fire at 65,000 psi or over. This is 10,000 psi higher than its intended use. This can cause primers to back out or cause harm to the rifle and the operator. Over and under-pressuring the chamber of your firearm can lead to a plethora of harmful malfunctions and should never be done. 

For a 5.56mm ammo, the standard loading is NATO SS109 (aka M855), which utilizes a 62-grain projectile. The powder charge for that round is fairly hot and is loaded to chamber pressures around 62,400 psi, but this can depend on barrel length and the type of action. Most ARs are chambered in 5.56 and .223. 

The History of These Rounds

The 5.56 x 45mm round was first developed in the late 1950s as an experimental cartridge for the U.S. Military M-16 rifle. This round was designed to have a small caliber and a high velocity. It was very desirable because the previous round that was used by the U.S. Army, the M-14 rifle, had weight and control issues with the rounds they used. 

The 5.56 x 45mm round was officially adopted as the NATO standard in 1963. The year after, Remington introduced a .223 caliber “civilian” version of the round. To this day, the .223 cartridge remains widely used by firearm enthusiasts around the country. The round is heavily nostalgic for gun-lovers because it is a descendant of the M-16 rifle. 

Remington also introduced the .222mm chamber in the company’s Model 722 bolt-action rifle. The chamber was based on a new rimless case, eliminating previous issues with the .22 Hornet and .220 Swift. It pushed a 50-grain bullet at an approximate 3,230 fps (reduced to 3,140 fps today). Quickly, it became the go-to for varmint and predator hunters. 

The chamber provided a long barrel life, little recoil, and high accuracy, some of the most crucial elements of a round. The .223 Remington has been renowned for decades now, even producing a near-perfect five-shot group at .009 inch by M.P. “Mac” McMillan in 1973.

The .223 Remington vs. the .222 Remington

.223 Remington began to be mass-developed in 1957, and it became available to the public in 1964. This was a month before the U.S. military adopted its twin cartridge, the 5.56mm Ball, M193 for the AR-15 and M-16 rifle. The case was modeled after a lengthened version of the .222 Remington that offered more powder capacity and velocity. It was rejected by the military but did huge numbers commercially.

The .223 Remington rapidly outsold the .222 Remington and its next best competitor, the .222 Remington Magnum. Within months, both the 222 Remington and the .222 Remington Magnum began dropping in popularity. Today, the .223 Remington is by far the most widely used centerfire varmint cartridge worldwide.

In February 1964, the U.S. military introduced the M193 Ball cartridge, essentially the same cartridge as the .223 Remington, except it was loaded with a 55-grain FMJ bullet at around 3,250 fps. Between 1977 and 1980, Fabrique Nationale adjusted the military loads’ specifications under the guidance of NATO. This new cartridge would become known as the 5.56x45mm NATO, or in short, the 5.56 NATO. 

Choosing the Best Option For You

There are many factors to consider when deciding what caliber of firearm you want. Decide what type of shooting style you want to pursue and what purpose you have for purchasing a rifle. Are you a hunter or a range shooter? If you’re a hunter, what kind of game do you hunt? 

Overall, the .223 Remington chambering is a safer, all-around choice. It is ideal for both range shooting, as well as for competitions. You can even hunt as well. Compared to the 5.56 NATO, the .223 can load heavier for hunting and varminting. Also, because of the .223’s slower twist rate and shorter leade, it will probably be more accurate at long-range.  

As for the 5.56 NATO, you may be able to get a higher pressure shot, but in terms of accuracy and practical use, it is definitely inferior to the .223 Remington. In addition, there are much fewer loadings available commercially and it is also more expensive. Some rifle owners enjoy the ability to say that their gun uses military-spec ammo. However, for real-life use, there aren’t many advantages. 

In Conclusion

Most beginners in the firearm world have no clue what the difference is between .223 Remington and 5.56 NATO ammo. This lack of information has become so pervasive that a misconception has been popularized that these two ammo are interchangeable. Think again! You cannot use these ammo interchangeably, and doing so is wildly dangerous. 

These two AR-15-built chambers have been used by our military and by citizens across the country for decades. One main difference between the two is the temperature of the rounds. 5.56mm ammo is a little bit hotter than .223mm ammo. 

There are also variances in powder charge, projectile, and rifle specifications between the two ammo. Before you load your gun, always confirm what loadout your AR-15 is chambered for. These specifications differ between rifles. 

Your performance as a shooter is dependent on your competence when loading and setting up your firearm. Remember, safety is your number one priority. Shooting guns is fun, but it’s also extremely dangerous. Always use the specific ammo that your gun is chambered for. There are no exceptions to this rule.

Now that you have educated yourself about these two kinds of ammo, you’re ready to choose what caliber you want. Get out there and go shoot! 

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