Just What Is The Difference Between .223 Rem. and 5.56 Nato???

Some ARs shoot .223 ammunition. Others fire only 5.56mm. Still others chamber both. You can fire a .223 from a 5.56 gun but you’re advised not to do the opposite. Most shooters understand that. The reason why may be lost on some though. What exactly is the difference?

AGG.com featured a video article on the differences: .223 vs. 5.56. Please look at their article and watch the following video.

.223 Vs. 5.56

There are certain performance characteristics between the two nearly identical rounds. The primary differences are: 5.56 is a higher pressure round and a .223 bullet is just a hair smaller than a 5.56.

That’s why you can run a .223 through a 5.56 gun but not the other way around. If in doubt (and in the market) buy a gun designed for both.