A common question regarding ammunition is often “What is the difference between .223 Remington and 5.56 NATO?” Well ask and you shall receive! Let’s go through the similarities and differences between .223 vs. 5.56 to help you differentiate and understand the two.
Introduced in 1964, the .223 Remington was a commercial cartridge that was derived from its predecessor the .222 Remington. It is loaded with a .224 inch diameter jacketed bullet and has weights ranging from 40-90 grains with the 55 grain being the most commonly used. Derived from the .223 Remington, the 5.56 NATO, originally chambered in M16 rifles, is a standard cartridge for NATO forces. The round was adopted to replace the weight and control issues associated with the 7.62×51 round. Since the .223 Remington was a civilian used round, and was registered with SAAMI, it could not be changed to fit military needs and thus the 5.56 NATO was born.
I bet at first glance of the picture above, you could not tell which kind of bullets were displayed; are they 5.56 or .223? This is because the external dimensions of the .223 and 5.56 are pretty much the same, with the specifications of the commercial brass cases being identical. The cases measure almost the same capacity with the only differences seen from brand to brand. Since the brass is virtually the same as far as shape, the difference in the two rounds lies in pressure and throat lengths.
The organization known as SAAMI or the Sporting Arms and Ammunition Manufacturers’ Institute, sets industry standards for ammunition, firearms and components. SAAMI has standardized the .223 but not the 5.56. The 5.56 standards are set by the military, and because the two rounds have different organizations standardizing them, pressures are measured differently between the two. Since pressure is measured differently, it is not possible to make a comparison. Instead you would be required to test both using the same chamber, and methods to see differences. As a general consensus, 5.56 may be loaded to higher pressures than .223.
Another difference between the two is the longer throat dimensions on the 5.56 NATO. The “throat length” refers to the distance between the end of the cartridge neck and the spot where the rifling in the barrel engages the bullet. The military loading uses a heavier casing which has resulted in the lengthening of the throat in the 5.56 chamber since increasing length is the only way to increase weight while using the same materials. With this new configuration, .223 Remington can be safely fired from a 5.56 chambered gun, but because 5.56 NATO may produce pressures that exceed the .223 SAAMI limits it is not advised to fire 5.56 from a .223 chamber. In short, this means the .223 Remington can be safely fired from a 5.56 stamped barrel but a 5.56 NATO should not be fired from a .223 stamped barrel.
Choosing between the two types of ammunition depends a lot on what you plan on using it for. With a longer throat, the 5.56 is more accurate at long distances compared to the .223. On the other hand 5.56 has a reputation of not being as accurate as the shorter throated .223. Generally speaking, the rounds do not differ a whole lot in terms of recoil and accuracy unless you are really shooting for max accuracy. So what it really comes down to is what kind of barrel you have, and what you want to shoot!