I’ve got an AR-15, what Ammo should I Shoot?

By Kurt Darrell

AR-15 .223 vs Mil-Spec 5.56mm Chambers


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Among AR-15 enthusiasts, there is a long-standing debate over whether someone should choose the .223 chambering or the Mil-Spec 5.56mm chambering for their AR-15 rifle platform. Aren’t these two different names for the same round, or is there a real difference? If so, which chambering should you go with? Let’s take a closer look at the issue.


A Brief History

The .223 and 5.56mm rounds have a long and complicated history. For now, we can simply say that the famous M16 assault rifle began its life in the U.S. military as the AR-15, which initially used a .223 Remington round. Because the U.S. military decided to switch to metric designations, the 5.56×45 mm NATO became the standard round used in the AR-15. Through the course of various field tests and experiments, the AR-15 evolved into the M16 to reflect the military’s needs and expectations.

After this, Remington continued to sell the .223 Remington round commercially. Today we see both round types and chambering configurations available to AR-15 enthusiasts. How significant is the difference between the two types? And what are their differences?


Differences in Chambering

As a serious ammunition expert will tell you, the .223 and 5.56mm seem like the same bullet, but the differences between the two are significant enough that you should pay attention to them. First of all, the 5.56mm round produces a higher chamber pressure than the .223 round, due to its hotter load.

Combine this with the fact that Mil-Spec 5.56mm chambers are slightly larger and have longer throats to account for the increased pressure of the 5.56mm round. What all of this means is that it is safe to fire .223 rounds with Mil-Spec 5.56mm chambering, but it is not a good idea to fire 5.56mm rounds with .223 chambering.

Mil-Spec 5.56mm chambers are built for high pressure and can take lower pressure rounds like the .223, but .223 chambers are not built for the higher pressure that 5.56mm rounds produce. Pressure build-up from firing 5.56mm rounds in .223 chambers can eventually cause damage to your AR-15, and it can even pose a danger to the shooter and those around the shooter.


What Should You Do?

The chambering dimensions that are most right for you should depend on what you want out of your AR-15 rifle. Since the Mil-Spec 5.56mm chambers can accommodate the 5.56mm round and the .223 round, they are a great choice for shooters looking for versatility, and the ability to use different types of ammo in their rifles.

However many shooters prefer specific .223 chambering and are only looking to use .223 rounds for their lower recoil, affordability and availability, and competition-friendly characteristics.

The right AR-15 components for you should depend on your shooting preferences, ammunition shopping needs, and loading preferences. However, remember that weapons experts don’t recommend shooting 5.56mm rounds with .223 chambering, and that doing so can be unsafe.

Author Bio: Kurt Darrell is a contributor for several websites dealing on different kinds of topics. When he is not working, he can be found gardening, windsurfing, hiking, or working on his upcoming blog that he will be publishing soon.

Image 1: https://en.wikipedia.org/wiki/File:223_Remington.jpg

Image 2: https://en.wikipedia.org/wiki/File:GP90.jpg

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