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The Topic of 5.56 NATO, .223 Remington and .223 Wylde Can Take You Down Some Pretty Wild Rabbit Holes – But Here’s What the Difference Is, and Why It Matters

by Richard Baimbridge

When it comes to AR-15 rifle chambers, the gold standards are of course 5.56 NATO and .223 Remington. But if you hold the two cartridges up side by side, they appear to be identical – so much so, in fact, that many people use them interchangeably, despite rumors of someone’s distant uncle who blew up his gun that way. Adding to the confusion is the fact that, initially, they were basically the same thing… But today there are some critical differences, as we’ll soon see.

Remington first created the .223 in the 1950s to meet the military requirements for adopting the AR-15 platform, which was designed around their commercial .222 varmint round – the first civilian rimless cartridge produced in the USA. Based on military specifications, the cartridge was lengthened and given more powder. It was then called the .222 Special, and later Remington .223.

In 1963, a 55-grain Remington-designed bullet on the .223 Remington cartridge was officially designated as 5.56 mm Ball M193 by the US Armed Forces. And in 1980, NATO adopted its own version of the 5.56 (modified a decade earlier by Belgian company FN), the NATO 5.56x45mm, which is the standard for today. 

The differences between .223 and 5.56, depending upon whom you ask, range from significant to basically nothing more than just the name. Trying to fully understand this topic can take you down a rabbit hole with more twists than quantum physics or an episode of The X Files – it’s something you can (and many people have) truly geek out on in terms of ultra-precise measurements and ballistics firing tests.

One of the most significant differences between the 5.56 and .223 cartridges is the chamber pressure. The NATO 5.56x45mm cartridge operates at a higher pressure (around 58,000 psi on average) versus the .223 Remington (averaging around 55,000 psi).

This difference can affect the performance and safety of the ammunition when fired in different chambers. 5.56 chambers have a longer throat (aka “freebore”) than .223 chambers. This is the smooth part of the barrel just before the rifling begins. So, while you can shoot a 5.56 round from a .223 Remington chamber, it puts a lot of stress on the gun and isn’t recommended, with catastrophic failure certainly being possible. 

While 5.56 has better stopping power, the .223 is sometimes preferred by hunters, although it is considered illegal for big game hunting in some states that require high calibers. It’s perfectly safe to shoot .223 from a 5.56 chambered gun, but accuracy is often diminished. And this is where a man named Bill Wylde comes into the picture.

A gunsmith from Greenup, Illinois who specialized in precision rifles, Wylde compared both cartridges and realized that because they shared identical case dimensions, specifications from both chamberings could be combined in order to achieve the best of both worlds.

Wylde developed the chamber (and it is a chamber, mind you, not a type of ammunition) to safely fire both 5.56 NATO and .223 Remington rounds with high accuracy. By combining the leade angle of the 5.56 NATO chamber and the tighter .2240-inch freebore of the .223 Remington chamber, the .223 Wylde accommodates both without any concerns of over-pressurization, loss of accuracy or muzzle velocity stemming from a wider freebore.

Though in the past, AR-15s chambered in .223 Wylde were more costly, today the price gap has largely disappeared. So, it offers added versatility to your gun with basically no downside. In terms of rounds for everyday use, .223 Remington is also often easier to find and more budget-friendly than 5.56 NATO equivalents, which is another reason for its popularity.

So, if you’re in the market for a new AR-15, definitely consider .223 Wylde chamber as an option. It’s basically like getting two guns for the price of one…just don’t ask them where the .223 Wylde caliber ammunition is.

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