.223 vs. 5.56 (The Evil Black Rifle)

assault rifle

I am asked on a daily basis about the difference between .223 & 5.56 EBR’s (Evil Black Rifles). The questions run the gambit from, “Is it safe to shoot 5.56 ammo out of my .223 AR?” to, “ What is a .223/5.56 barrel?” It’s hard to wade through the opinions and hyperbole to get a straight, informed answer that isn’t stuffed with “expert” analysis.

The answer is really not all that complicated, so let’s break it down, get into some specifics, wade through a little bit of the techno-babble and, hopefully, put an end to the craziness and confusing surrounding one of the most popular shooting platforms available on the market today.

Here’s what Wikipedia has to say about the .223:

The .223 Remington is a sporting cartridge with almost the same external dimensions as the 5.56×45mm NATO military cartridge. It is loaded with a 0.224-inch (5.7 mm) diameter jacketed bullet, with weights ranging from 40 to 90 grains (2.6 to 5.8 g), though the most common loading by far is 55 grains (3.6 g).

While the external case dimensions are very similar, the .223 Remington and 5.56x45mm differ in both maximum pressure and chamber shape. The maximum and mean pressures for some varieties of the 5.56 mm (different cartridge designations have different standards) exceed the Sporting Arms and Ammunition Manufacturer’s Institute (SAAMI) maximums for the .223 Remington, and the methods for measuring pressures differ between NATO and SAAMI.

The 5.56 mm chamber specification has changed since its adoption. The current military loading (NATO SS-109 or US M855) uses longer, heavier bullets than its predecessor. This has resulted in a lengthening of the throat in the 5.56mm chamber. Thus, while .223 Remington ammunition can be safely fired in a 5.56 mm chambered gun, firing 5.56mm ammunition in a .223 Remington chamber may produce pressures in excess of even the 5.56mm specifications due to the shorter throat. In other words, you’re probably better off not not firing 5.56mm in a .223 Remington chamber! (hint, hint)

This is right on target (pun intended) as an excellent exposé on why, if you have a .223 barreled EBR you should shoot only commercial ammo and stay away from the mil-surplus stuff. If you have a .223/5.56mm barreled EBR or one that is only marked “5.56mm” then you are able to shoot either the commercial .223 or the mil-surplus 5.56.

I hope this helps explain the difference.