The age-old question, is 5.56x45 NATO vs .223?
5.56x45 vs .223? The question has been asked time and time again. With responses ranging from “the difference is so small it doesn’t matter” to an in-depth explanation of the difference in the two. First, I think one would need to understand the origin of each. I wonder if I have been asking the right question all this time?
The history of the 5.56x45 NATO round is well talked about as it was developed for the US Military in the search for small caliber high velocity weapon to replace the M14 (7.62×51mm). Scaling down this rifle cartridge to fit the militaries needs meant a soldier could carry twice the amount of ammo for the same weight. The .223 round was originally introduced to the military but not accepted, at this time it was known as the .222 Remington Magnum. It was meant for small mid-western Varmints and used by civilians. However, during testing to develop ammunition that would specifically meet the requirements of NATO that would penetrate through the side of the WWII US M1 Helmet at 800m, its predecessor the 5.56x45 won the bid. In 1962 the .223 Remington ammunition specifications were submitted to SAAMI, and it has since been held to those parameters.
The question you should be asking yourself is “what rifle am I shooting this ammo from, and why?”
While the barrel chamberings of .223 Remington and 5.56x45 NATO are not the same, we have been informed that it is safe to fire .223 Remington ammunition from an M16. Rifles chambered in .223 generally have a slower twist and a shorter lead. This creates a tighter freebore, if you tried to load that same rifle with a higher-pressure round like that of the 5.56x45 the results could be catastrophic. The barrel for that .22 caliber rifle was not designed to withstand that. The cartridges may seem identical, nonetheless they differ in powder load, bullet weight and chamber pressure. The throating or lead of the M16 is wider and longer, accompanied by a faster twist.
It wasn’t until Bill Wylde compared the two rounds and created a more accurate chamber to fire ammunition that supported NATO requirements as well as SAAMI regulations known as the .223 Wylde. This is the ONLY .223 chamber that can successfully fire a 5.56x45 NATO round. Generally, a rifle that shoots only .223 ammunition will have a 1:9 twist and uses a high grain round from 69 grains to 85 grains. A military grade 1:7 barrel is best accompanied with 62 grain ball or 77 grain tracer ammunition. All in all, your ammunition should be based on your rifle and not the other way around. Hopefully this information helps you as much as it has helped me. Now I can at least suggest we ask a different question when this topic comes up next, as we know now it’s not about one being better or worse than the other.