5.56 vs .223: What’s the Real Difference Between These Popular Cartridges? 

Two of the most popular cartridges today are nearly identical and sometimes considered transposable, but when looking at 5.56 vs .223, there are some key differences. The .223 Remington started as a military cartridge in 1957 — adapted from the .222 Rem. — but has been a popular hunting, sporting, and target cartridge ever since. The 5.56mm NATO cartridge was derived from the .223 Rem. as a dedicated service rifle cartridge by FN about 20 years later. Today, it’s common to see rifles chambered for both, especially AR-15 variants. And it is equally common to see ammunition in both chamberings next to each other on store shelves. But they aren’t exactly the same. Here’s how they are different and what you need to know on 5.56 vs .223.

5.56 vs .223 Specs

.223 Remington Specs

• Bullet Diameter: 0.224 inches
• Case Length: 1.76 inches
• Overall Length: 2.26 inches
• Parent Case: .222 Remington
• Case Capacity: 28.8 grains H2O
• SAAMI Spec Freebore Distance: .025 inches
• SAAMI Chamber Pressure: 55,000 psi

5.56x45mm NATO Specs

• Bullet Diameter: 0.224 inches
• Case Length: 1.76 inches
• Overall Length: 2.26 inches
• Parent Case: .223 Remington
• Case Capacity: 28.5 grains H2O
• SAAMI Spec Freebore Distance: .050 inches
• SAAMI Chamber Pressure: 61,000 psi

Key 5.56 vs .223 Differences

Though the 5.56mm NATO and .223 Remington cartridges are essentially identical externally, there are two key differences. First, the 5.56mm NATO is loaded to higher chamber pressures — 61,000 psi vs 55,000 psi. The second difference isn’t in the cartridge itself, but in the chamber specs. The standard 5.56mm chamber has .025-inch longer freebore distance than the .223 Remington. This is the distance from the case neck to the beginning of the leade — the gentle cone that funnels the projectile into the rifling. A shorter freebore with the higher-pressure loads can sometimes cause pressure to spike beyond the 61,000 psi standard or, in other words, create higher pressures than the 5.56 NATO is supposed to produce. In standard chambers or modern production firearms, this usually isn’t a problem. But freebore distances among chamber reamers can vary wildly so it’s always best to use caution or avoid shooting 5.56mm NATO in .223 Rem.

History

Remington Arms officially submitted the .223 Remington cartridge design to SAAMI in 1962 after several years of research and development in conjunction with the U.S. Continental Army Command, Fairchild Industries, and Eugene Stoner of Armalite. The work with Stoner was significant due to his primary role in the invention and implementation of the AR-10 platform. Their shared goal was to create a lightweight cartridge and rifle combination that provided acceptable terminal ballistics at extended distances on a more nimble platform compared to the AR-10 chambered in 7.62x51mm NATO. 

The result was Armalite’s AR-15 rifle, chambered in .223 Remington, propelling a 55-grain bullet at 3,250 fps. Two years after its submission to SAAMI, the U.S. Army adopted Armalite’s AR-15 rifle, dubbed the M16. The M16 first saw combat in the Vietnam war and went on to become the standard military issued service rifle in 1969. Since then, the .223 Remington cartridge has expanded to shooting endeavors from hunting to competitive shooting and everything in between. The success of the .223 Remington also extends beyond its AR-15 roots and it is chambered in a wide variety of rifle configurations.

Following the success of the .223 Rem., NATO signed an agreement in 1977 to begin the selection process of replacing the 7.62x51mm NATO cartridge. FN Herstal answered the call, developing the 5.56 NATO cartridge, which only slightly differentiated itself from the .223 Rem. That difference between the two cartridges came in the form of thicker walled brass which created a slightly smaller case capacity for the 5.56 NATO cartridge. This reduction in case capacity creates higher pressures and increased velocity from similar charge weights.

For comparing 5.56 vs .223, the 5.56 NATO has a maximum of 61,000 PSI of chamber pressure while the SAAMI approved chamber pressure for the .223 Rem. is 55,000 PSI.

By late 1980, NATO officially adopted and standardized the 5.56 NATO cartridge. Fast forward 40 years and the 5.56 NATO continues to be one of, if not the most, used cartridge amongst military forces worldwide. That fact alone speaks volumes to the validity and effectiveness of the cartridge.

5.56 vs .223 Twist Rates

As a standard, 5.56mm NATO and .223 Rem. rifles have different twist rates, and are intended to shoot different weight bullets. That has changed in the past couple decades, but more on that in a second. The .223 Remington was designed around shooting 55-grain bullets and used a twist rate of 1:12 — 1 revolution per 12 inches of barrel. This is ideal for those bullets, but limits the cartridge to lighter projectiles. Even today, reloading manuals such as Hornady’s top out at 62-grain bullets for .223 Rem. In 1980, a dramatically faster 1:7 twist rate was adopted for the 5.56mm to handle heavier, longer projectiles. A 1:7-twist barrel works well with even 80- and 90-grain bullets that are too long to fit in a standard AR-15 magazine.

As AR-15 rifles began taking over in service rifle competition, shooters began adopting tighter 1:8- and 1:7-twist barrels to take advantage of ballistically superior bullets. This is a reason why heavier-bullet load data for the .223 is listed under a separate service rifle section in some reloading manuals. Though some sporting .223 Rem. production rifles still have slow-twist barrels, most gun makers have adopted 1:7 or 1:8 to accommodate a wider variety of bullets.

The .223 Wylde

Lots of 5.56 NATO ammunition is commercially available, and as a universal solution to the discrepancy between 5.56 and .223 chambers, several rifle manufacturers began chambering rifles in .223 Wylde, which was developed by Bill Wylde. The Wylde slightly altered the chamber dimensions to accommodate the pressures created by both 5.56 NATO and .223 Rem. ammunition. Also, despite the warnings, many shooters freely shoot 5.56 NATO ammunition out of their .223 Rem. chambered rifles without issue. I discuss this in my extensive review of the best 5.56 ammo and .223 ammo test. If you want to fire 5.56 NATO ammo through your .223 chamber, proceed carefully and watch for any excessive pressure signs. If you’re buying a new gun or barrel, you can eliminate any potential ammo and pressure issues by purchasing a .223 Wylde or 5.56 NATO. An example of a fine .223 Wylde-chambered rifle is the NULA Model 20S, that I reviewed.

Ballistics

Comparing ballistics between the 5.56 vs .223 reveals only small differences. To compare apples to apples, I selected two factory loads from Winchester, both of which are loaded with a 55-grain FMJ projectile.

Winchester 223 Rem. 55-grain FMJ

• Muzzle Velocity: 3240 fps
• Energy @ 300 yards: 552 ft-lb.
• Drop @ 300 yards: 11.4 inches (with 100-yard zero)

Winchester 5.56 NATO 55-grain FMJ

• Muzzle Velocity: 3270 fps
• Energy @ 300 yards: 612 ft-lb.
• Drop @ 300 yards: 10.7 inches (with 100-yard zero)

However, muzzle velocity and downrange energy will vary depending on your bullet selection. Projectile weights range from 35 grains on up to 85 grains with 55- to- 62-grain bullets being the most popular. For comparison, I selected ammunition loaded with light, mid-weight, and heavy bullets to highlight differences in ballistics and the versatility of the two cartridges. 

Hornady 223 Rem. 35-grain NTX Superformance

• Muzzle Velocity: 4,000 fps
• Energy @ 300 yards: 411 ft-lb.
• Drop @ 300 yards: 5.3 inches (with 200-yard zero)

Nosler 223 Rem. 55-grain Ballistic Tip Varmint Ammunition

• Muzzle Velocity: 3,100 fps
• Energy @ 300 yards: 533 ft-lb.
• Drop @ 300 yards: 7.7 inches (with 200-yard zero)

Barnes 5.56 NATO 85-grain Precision Match

• Muzzle Velocity: 2,600 fps
• Energy @ 300 yards: 745 ft-lb.
• Drop @ 300 yards: 11.5 inches (with 200-yard zero)

These three ammunition offerings paint a valuable picture for understanding the differences in muzzle velocity and downrange energy that is obtainable with the .223 Rem. and 5.56 NATO cartridges. 

Recoil

Recoil, or the lack thereof, from these two cartridges is one of their biggest selling points and tremendously aids their popularity. The vast majority of 5.56×45 ammunition produces between 5 and 6 ft-lb. of recoil. In simple terms, the recoil produced from these two cartridges is negligible. This allows shooters to stay on target, watch bullet impact and make quick follow-up shots if necessary. 

Accuracy

Both the .223 Rem. and the 5.56 NATO are easy to shoot and capable of delivering exceptional accuracy. With that said, accuracy with these two cartridges can and will vary depending upon your rifle and ammunition selection. Pay attention to the twist rate of your barrel and match it with appropriate-weight bullets as described above.

5.56 vs .223 Accuracy Myths

The 5.56mm NATO, .223 Rem., and .223 Wylde are all capable of great accuracy, but there are various myths about all three. The biggest myth is that you will see worse accuracy when firing .223 Rem. ammo through a 5.56mm NATO chamber because of the longer freebore. While this can be true in some cases, it probably has more to do with the barrel quality and/or chambering job. There are many examples of 5.56mm NATO rifles shooting .223 Remington ammo just as accurately as 5.56mm ammo from the same gun — or with better accuracy. One example is the Savage M110 Trail Hunter Lite that I reviewed, which is chambered in 5.56mm. It showed better accuracy with .223 factory (and .223-pressure handloads) with 52-, 55-, and 77-grain bullets than with 5.56mm NAT0 factory (and 5.56mm NATO pressure handloads) using 77-, 80-, and 85-grain bullets. The previously mentioned NULA 20S, which has a .223 Wylde chamber and 1:8-twist barrel shot .223 Rem. loads more accurately than 5.56mm NATO loads — even with the same bullets.

Terminal Performance

When it comes to evaluating the 5.56 vs .223, both pack plenty punch to deliver adequate terminal performance in a variety of hunting pursuits. However, given the small diameter and bullet weights, hunters must be conscious of the cartridge’s limitations in hunting scenarios. With a well-constructed bullet, such as Hornady’s 50-grain monolithic CX bullet or Nosler’s 70-grain Accubond, hunters can confidently take down deer-sized game at reasonable ranges with the .223 Rem. and 5.56 NATO. Shot placement is key, especially when shooting small projectiles. Effective options for hand loaders are Sierra’s 77-grain TMK and Hornady’s 80-grain ELD-X. These cartridge and bullet combinations are ideal for recoil shy and first-time hunters.

While the .223 Rem. and 5.56 NATO are plenty capable in the deer woods, they really shine in the varmint hunting world. Unlike the bullets necessary for taking down a deer, the majority of varmint hunting projectiles are designed to penetrate the thin skin of a coyote or fox and inflict massive amounts of internal trauma. The result is dead-on-impact hits that rarely require a tracking job. 

Ammunition Availability and Selection

Ammunition availability for the .223 Rem. and 5.56 NATO has been hit and miss over the past several years, but manufacturers currently produce copious amounts of ammunition for these two cartridges, which is readily available both online and in most sporting goods stores.

The cost of .223 Rem. and 5.56 NATO ammunition varies depending on its intended use. If you are just looking to plink steel at the range, cheap M193 full metal jacket ammunition can be purchased for as little as $13 per box of 20. On the flip side, ammunition loaded with premium hunting and match bullets can run upward of $60 per box of 20. 

Unlike many other cartridges, 5.56 and .223 ammo is often available in bulk. Most major ammunition companies package 5.56 ammo that can be purchased in case quantities of 200, 500, or 1,000 rounds. Buying in bulk typically saves you money in the long run.

Read Next: Coyote Cartridges: .223 Rem. Vs. .22-250 Rem. Vs. .243 Win.

Are .223 and 5.56 interchangeable?

Yes, but with a caveat. It’s fine to shoot .223 in a 5.56mm chamber, but not advised to shoot 5.56mm NATO in .223 chambers because there is a chance it will produce dangerous pressures.

Are .223 and 5.56 magazines interchangeable?

Yes, externally, the two cartridges have the same dimensions, so a 5.56mm magazine will work for .223 and vice versa.

Does and AR-15 shoot 556 or 223?

Many AR-15 rifles shoot 5.56, but many also shoot .223. It all depends on the barrel. Some which have a .223 Wylde chamber will safely handle both.

Does the military use .223 or 5.56?

The United States military used to use .223, but uses 5.56mm NATO now.

Final Thoughts on the 5.56 vs .223

While the .223 Rem and 5.56 Nato are similar, it is important for gun owners to educate themselves on the nuances of both cartridges and at least be aware of the difference in chamber pressures between the two. If you choose to shoot 5.56 NATO ammunition through a .223 Rem. chambered rifle, you must vigilantly watch for any and all signs of excess pressure. Regardless of your shooting pursuits, everyone should own a rifle chambered in one (or both) of these cartridges. They are practical and capable of everything from hunting to personal defense. Plus, they are downright fun to shoot.