The .223 Remington and 5.56x45mm NATO are two of the most popular rifle cartridges in the world, widely used by civilian shooters, military forces, and law enforcement agencies. Despite their similar dimensions, these two cartridges have important differences that affect their performance, safety, and use in various rifles. This article will explore the key differences and similarities between the .223 Remington and 5.56x45mm NATO, providing a clearer understanding of their applications and compatibility.
Origins and Development
The .223 Remington was developed in the late 1950s by Remington Arms, primarily for civilian use and varmint hunting. It was introduced commercially in 1964 and quickly gained popularity among shooters due to its accuracy, low recoil, and versatility. Soon after, it was adopted for military use in a modified version, which became the 5.56x45mm NATO.
The 5.56 NATO cartridge, standardized by the North Atlantic Treaty Organization (NATO) in the early 1980s, was designed for use in military rifles like the M16 and later the M4 carbine. It was intended to offer soldiers a lightweight, high-velocity round with improved penetration and performance at longer ranges compared to earlier rifle cartridges like the .308 Winchester (7.62x51mm NATO).
The top performer for the US Military and preferred 5.56x45mm would be the MK262 MOD 1-C from Black Hills.
“Back in 1999, at the request of the U.S. Navy we began the process of developing the 5.56mm military precision round. Eventually, after extensive development and even more extensive field testing, that idea became the only one of its kind fielded and used with great effect by the greatest military in the world.
Like the original, the new MK262 Mod1-C commercial round features the exact construction and performance specs of the U.S. Military round. It is now available in military ammo cans containing 460 rounds in 20 round cartons.
And in the spirit of pushing limits, these rounds come with the same no-nonsense lot acceptance accuracy test (10 groups of ten shots each at 300 yards) provided on military lots. No lot will ship unless it shoots sub 2″ groups (.64 MOA maximum/10 shot groups).
Our company’s story is rooted in the performance and dependability of this unrivaled round. It was designed to do the most important job in the world. Protect our freedom. And we built it to do just that.” – Black Hills on the MK262 MOD 1-C
Key Differences: Pressure and Performance
Although .223 Remington and 5.56 NATO cartridges are nearly identical in size, they differ in the internal pressures they generate, which directly impacts performance and safety in specific firearms.
- Chamber Pressure: The 5.56x45mm NATO operates at a higher chamber pressure than the .223 Remington. The standard pressure for a 5.56 NATO round is approximately 58,000 psi, while the .223 Remington is typically loaded to around 55,000 psi. This difference in pressure can have implications for firearm safety, especially when firing 5.56 NATO rounds in a .223 Remington chamber.
- Throat and Leade: Another important difference between the two cartridges lies in the rifle chamber dimensions, particularly the “leade” or the distance between the end of the cartridge case and the rifling in the barrel. The 5.56 NATO chamber has a longer and more gradual leade, which allows the bullet to travel slightly farther before engaging the rifling. This helps accommodate the higher pressures of the 5.56 NATO round. Conversely, the .223 Remington chamber has a shorter, tighter leade, which is optimized for the lower pressures of the .223 Remington cartridge. Firing 5.56 NATO ammunition in a rifle chambered for .223 Remington can result in increased chamber pressure, potentially leading to reliability issues or even catastrophic failure. This is why 5.56 NATO rounds should not be fired in rifles specifically chambered for .223 Remington unless the rifle is explicitly rated for both cartridges.
Interchangeability and Rifle Markings
Due to their external similarities, many shooters assume that the two cartridges can be freely interchanged, but this is not always the case. It is essential to understand the markings on a rifle barrel to determine what ammunition is safe to use:
- Rifles marked “.223 Remington” are designed to handle .223 Remington ammunition and are not rated for the higher pressures of 5.56 NATO rounds. Firing 5.56 in these rifles can cause excessive wear, pressure spikes, or damage over time.
- Rifles marked “5.56x45mm NATO” or “5.56 NATO” are designed to handle both 5.56 NATO and .223 Remington rounds safely. These rifles have a longer leade and are built to withstand the higher pressure of 5.56 NATO ammunition.
- Rifles marked “.223 Wylde” or other hybrid chamberings are specifically designed to handle both .223 Remington and 5.56 NATO ammunition without issues. The .223 Wylde chamber combines features from both the .223 Remington and 5.56 NATO chambers, making it a popular choice for versatility.
Ballistics and Applications
The ballistics of .223 Remington and 5.56 NATO rounds are quite similar, with both cartridges delivering flat trajectories, low recoil, and impressive velocities. However, because of its higher pressure, the 5.56 NATO typically achieves slightly higher muzzle velocities and better terminal performance, especially at longer ranges, but not completely true. Many smaller loading companies are now loading .223 Remington in NAS3 cases. Take Badlands for example, the 85gr Match Burners.
Both rounds are excellent for target shooting, varmint hunting, and home defense, but the 5.56 NATO is often preferred for military and tactical applications, where its enhanced penetration and reliability at range make it the more effective choice, specifically the 77gr OTM Mk 262 MOD 1-C from Black Hills.
Conclusion
The .223 Remington and 5.56x45mm NATO cartridges are closely related but not identical. Understanding the differences in chamber pressure, throat dimensions, and rifle compatibility is critical to ensuring safe and effective use. While 5.56 NATO rifles can safely fire both cartridges, .223 Remington rifles should only fire .223 rounds to avoid potential issues. Both .233 and 5.56 fit the same magazines and AR15 magazine carriers. For those seeking versatility, rifles chambered in .223 Wylde offer the best of both worlds, providing the ability to shoot either cartridge without compromise. If you want to read more about this subject check out .223 Remington and 5.56x45mm NATO at Ammo.com.
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