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What Is The Difference Between 223 And 556 Ammo – A Comparative Review

In this article, we will be providing an in-depth review of the similarities and differences between .223 and 5.56 ammunition.

A lot of people, especially novices, have an assumption that these two pieces of ammo can be interchanged, in reality, they are not.



In the 1950s, the 5.56 x 45 round made its debut and was developed as an experimental cartridge and tested on the U.S Military M-16 Assault Rifle. Ease of use and effectiveness was one of the major selling points of this round. It resolved problems like eased control and heavyweight which was regularly experienced in the 7.63 x 51 mm rounds that were utilized in the M-14.

When the military officially adopted the 5.56 x 45, the manufacturing company called Remington created their own civilian version of the 5.56. Giving birth to the 223 which is civilian version equivalent to the 5.56 military-grade round.

The 5.56 x 45 mm round first came about during the late 1950s as an experimental cartridge for the U.S. Military M-16 rifle. This “small caliber, high velocity” round was desirable because it helped overcome weight and control issues present in the 7.62 x 51 mm round that was used in the previous-generation M-14 rifle.

After the official adoption of the 5.56 x 45 mm round as the NATO standard in 1963, Remington introduced a .223 caliber “civilian” version of the round shortly thereafter in 1964.

A very popular sporting rifle for today’s enthusiasts is the AR-15. This firearm is commonly chambered for 5.56 mm ammo because it is a descendant of the M-16 rifle.



223 Ammunition

The 223 inscription on a bullet means that the bullet’s base diameter is .223 inches wide. Guns have specifications that guide you on the bullet size that is compatible for use with the specific gun. Ensure that you only load ammo that is supported by the gun you are using to avoid damaging the gun.

The “Rem” in 223 Rem is short for Remington, the ammunition and firearms company that originally developed the caliber in the 1960s.

5.56 NATO Round

When you go to buy rifle ammo, you will probably come into some that are labeled NATO rounds while others are not. The NATO stands for North Atlantic Treaty Organization that is a group of countries that have an agreement to standardize their ammo. NATO grade bullets are military grade and not meant for recreational use such as a hunting game or shooting sports. Their standards are for military combat situations. The standardization helps troops in the field to share ammo with allies that use the same standardized ammo.

Lower Pressures vs Higher Pressures

Selecting the right ammo to safely fire in your weapon is a result of various studies and testing methods. Here is some more information about pressure levels associated with these two rounds.

5.56 vs 223

The 5.56 has a higher pressure measuring at 58,000 psi as compared to the 233’s 55,000 psi. Going by SAAMI specifications, the lower pressure 223 can be used in the 5.56 chamber, but the 5.56 cannot be used in the lower pressure chamber for the 223 Remington.

The 5.56 also has a longer throat with a difference of .125 inches in length when compared with that of the 223 Remington bullet. The longer throat allows more holding capacity for gun powder in the 5.56, thus implying that it has a higher performance as compared to the 223 Remington.

223 vs 556 Ballistics

Although they are of the same size, the two bullets have different results when shot from a rifle. Note that the 5.56 cannot be shot on a 223 chamber but the 223 chamber can be shot from a 556 due to the pressure difference.

The 556 packs more pressure and gun powder, meaning that it travels faster and is more accurate. Although the 223 can be shot from the 5.56 chamber, it will attain a lower speed due to its lower pressure.

The 556 is also a little heavier, which means that the effect of the atmosphere on its trajectory is less than it is on the 223 trajectory. This means the 5.56 travels a longer distance when the two are shot in the same atmospheric conditions.

Ballistic Differences

Whereas PMC 5.56 NATO 55-grain ammunition has a velocity of 3,270 fps and produces 1306 ft/lbs of energy, and PMC 5.56 NATO 62-grain ammunition has a velocity of 3,100 fps and 1,323 ft/lbs of energy.

There are ballistic differences between the .223 Remington and 5.56 NATO rounds, but this is largely dependent on load selection.

223 Ballistics

External ballistic tests on the 223 using a standard 55gr bullet leaving the barrel at 3,215fps reveals that the 223 fps slows down by less than half of the velocity at a 500-yard distance. The energy loss at this point is about 1000 pounds. The bullet also drops about 64 inches due to gravitational pull. All this happens in .741 seconds.

These ballistics stats mean that the 223 is accurate and has less jump. The accuracy is enhanced by the shorter lead when the bullet moves from the case to the barrel.

223 vs 5.56 Stopping Power

The 223 Remington bullet is lighter and has less pressure in its chamber. The 5.56 is slightly heavier. Comparing the stopping power of the two bullets when fired from a 5.56 barrel means reviewing the impact of the velocity at which the bullet is travelling at when it stops. Leaving the guns’ barrel at the same speed will see the heavier 5.56 bullet drop faster than the 223. The 5.56 also maintains the higher velocity for longer, thus implying that the 5.56 velocity has a greater stopping power as compared to the 223 velocity.

In simpler terms, the stopping power means that the 5.56 will leave a larger bullet wound on the victim or target as compared to the 223 when they are fired from the same point.

223 vs 556 Ammo Trajectory

Testing results have proved that firing a 223 bullet from a 5.56 barrel alters the trajectory. This is attributable to the resulting higher jump and lead on the 223. Some barrels can compensate for these differences while others cannot.

Generally speaking, the trajectory change depends on the barrel on the rifle you will use. The barrel’s capability to compensate for jump and pressure changes will determine by how much the trajectory will be altered.

Highest Grain 223 bullet

The 223 has a wide range of bullet sizes that can fit in the chamber. You need to choose what is best for you under the conditions and what you are aiming at. Statistics have it that over 90% of bullets fired in the United States are for recreational purposes. For such situations, a typical 55-grain bullet would suffice. Higher grain bullets are available with the Remington having in stock 77 grain –OTM rounds that are typically used for military marksmen.

However, some 223 bullet weight can go up to 80 grains. These higher grain rounds do require use in a “throated” barrel due to their longer overall length. They simply can’t be run in a normal semi-automatic 223 rifle and instead must be used in bolt-action single-shot rifles.

5.56 NATO Bullet Drop

The bullet drop on the 5.56 over a range of 500 yards is 54.2 inches. The start sees the bullet drop a little to about 1.75 inches and maintains this height up to 300 yards where it drops a further 8.3 inches. At 400 yards out, the drop is 24.56 with the 500-yard mark, making for the 54.2 inches drop.

5.56 NATO Dimensions

The 5.56 bullets measure 2.260 inches in overall length with the case measuring 1.760 inches. The bullet has a diameter of 0.224 with the neck measuring 0.253 in diameter.

The base of the bullet has a diameter of 0.377 inches. The case capacity for packing firing powder on the 5.56 is 28.5 gr. The bullet packs pressure of up to 54,114 psi.

M193 vs M855

The main difference between these two rounds is that the M193 is 55g lead core and is surrounded by a copper jacket with a boat tail. M855 5.56 ammo is a 62g bullet that has a steel core. The M855 also packs a steel penetrator tip at the end that helps it to get through obstacles easily.

Though the M855 seems like a “better” choice for you to buy because of the penetrator tip, your shooting needs will determine what is best for you.

For distances less than 100 yards, 5.56 M193 ammo gives better performance (higher velocity) due to its lighter weight (plus, it’s cheaper in bulk than M855 ammo). For longer distances, however, go with the M855 with the penetrator steel tip in order to combat wind-drift.

Keep in mind though, M855 is more prone to tumbling or “keyholing” when it hits a target. This can cause the round to actually penetrate less deeply and shifting in the target in unintended directions.

This is important especially if you’re using the rounds to hunt wild game. A tumbling round can both miss vital organs needed to drop the target (like the lungs) while also destroying meat tissue or rupturing bowels.

223 Wylde vs 556

Due to the potential danger that comes with firing a 5.56 bullet from a 223 chamber, innovative design manufactures have come up with the 223 Wylde rifle chamber. This chamber enables the safe firing of the 5.56 bullet from a 223 Remington chamber. It does this by having an identical chamber angle with that of the 5.56 chamber and .224 diameter on the free bore. The free bore also gives a tight fit to the 223 bullets, thus enhancing the accuracy and handling of 223 bullets fired from it.

5.56 Effective Range

When fired, the 5.56 bullet covers a distance of more than 1000 yards. However, due to natural conditions that include gravitational pull, the atmosphere, wind, and the angle the bullet is fired from, the 5.56 velocity reduces beyond distances of 400 yards. The effective range for 5.56 bullets, therefore, is between 400 and 500 yards. In this range, the bullet will have maximum effect on the target. Beyond this, expect less impact on the target you are aiming at. The long range makes this a good projectile for the battle field because soldiers can aim and drop targets who are far away with effectiveness.

223 Effective Range

Similar to the 5.56, the 223 covers a long distance when fired from the gun’s barrel. The bullet starts losing altitude and velocity with time reducing the impact that the bullet has when it finally reaches the target. The effective range for 223 is 400 to 600 yards. This makes it perfect for shooting game in the woods without getting too near. Controversy covers the use of the 223 in civilian hands due to its ability to drop long-range targets with high accuracy. It is, however, marked safe for use in civilian hands.

5.56 Ammo vs 223 Accuracy

The 223 and 5.56 have the same size and are similar in most aspects. Both of these bullets are compatible with AR-15 bullet size specifications. SAAMI specs for each ammo size dictate the kind of rifle barrel that they should be fired from. It is imperative to note, however, that firing the bullets from the SAAMI specs recommended barrel does not have much of a difference in accuracy. However, if fired from the same 5.56 barrel, the accuracy of the 223 is altered slightly to make it less accurate.

In this regard the 5.56 comes out on top.

Case Size

The outer dimensions of the brass case for the 5.56 x 45 mm and the .223 are the same. However, there are many other factors that determine what is a safe round to chamber in a particular firearm, and although the case size is identical on these two rounds they are not interchangeable.


The 5.56 mm chamber has a longer distance between the mouth of the cartridge and the point at which the rifling engages the bullet. The .223 Remington chambering has a shorter distance before the rifling engages the bullet. This means that the pressure within the chamber that is produced when firing can be dramatically different for these two rounds.


Due to the differences in the chamber described above, a .223 round fired through a 5.56 mm chamber will result in lower pressure than what is safe for the firearm and is therefore typically safe. However, a 5.56 mm round fired through a .223 chamber will result in higher pressure than what is safe for the firearm and thus is not considered safe. This over-pressuring of the chamber can lead to all sorts of dangerous malfunctions and should be avoided at all costs.

What Can I Shoot in My Gun?.223 vs. 5.56: Cartridge Comparison

The .223 Remington is a sporting cartridge with the same external dimensions as the 5.56x45mm NATO military cartridge.

NATO uses 5.56mm test barrels designed to measure chamber pressure at the case mouth, as opposed to the SAAMI location.

What does all this mean to you? Quite simply, it means firing a 5.56mm NATO through a gun not designed for that round can be problematic.

For those interested, leade is the distance between the mouth of the cartridge and the point where the rifling touches the bullet.

The downside is that, at greater distances, some shooters think they will see a decrease in accuracy when shooting .223 Remington ammo through a 5.56 NATO chamber because the chamber is ever so slightly larger.

While for those who prefer a bolt-action rifle, there is no problem firing .223 Rem. ammunition from a chamber marked for 5.56 NATO; yet the AR-15 shooters may find that some rifles are set up to perform with the higher recoil level and pressure levels of the hotter 5.56 NATO ammo. I have seen instances where those rifles chambered for 5.56 NATO with heavier springs won’t reliably extract and feed .223 Rem. ammo; there simply isn’t enough oomph to properly cycle the rifle.

I wish the powers that be had decided on one universal design, so as to avoid the confusion that has developed from having two names—and power levels—for the same cartridge, but alas, we are left to deal with the mess. If you already own one or the other, please take note of this information. If you’re shopping for a rifle chambered for one of these cartridges, may this enlighten you before you make your purchase. Both the 5.56 NATO and .223 Rem. are sound designs, yet they are not one and the same. Forewarned is forearmed, so make your decision accordingly.

Can You Load 223 Rounds in a 5.56 Magazine?

A common question with gun users is the compatibility of two cartridges with firearm magazines. The simple answer is yes, you can load 223 rounds in a 5.56 magazine. Just be sure to note that the ammo loaded in the 5.56 Magazine is actually 223 Rem ammo.

The opposite is even more important. If you load 5.56x45mm NATO ammo in a magazine or clip that is typically used in a 223 Rem chambered firearm, be sure to note it on the magazine or clip! This is due to the higher pressure created when a 5.56 round is fired versus a 223 round.


After comparing the 223 vs 5.56 we can comfortably say that the two bullets are similar in most aspects. The 223 in civilian use offers great accuracy and precision when hunting while the 5.56 is a good projectile on the battlefield. You, therefore, must choose the bullet that suits your needs best depending on where you will be shooting.

Now that you know the differences between these two calibers, be sure you know how you should be stockpiling your ammo!

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