During the Vietnam War the United States Air Force, was test firing a new weapon with a new projectile. It was designed to revolutionize warfare. But at the time, was only designed for base security.
This was the invention of the 5.56 x 45mm NATO. This became the standard cartridge for the US Army and Marine Corps during the early stages of the Vietnam War.
It is derived from, but not identical to the .223 Remington cartridge.
At the Geneva Convention, NATO, the UN, and the United States all came to an agreement to use the same caliber for peacekeeping forces. Again, this was known as the 5.56mm NATO.
The United States underwent testing with this cartridge and originally had designed it only to be used as a Air Force base security weapon.
In its early stages, the .223 Remington cartridge was designed only for small vermin, killing nothing bigger than badgers, raccoons, coyotes, and other such animals of a similar size.
Originally, this cartridge was never designed to be used on the battlefield.
Let’s discuss some of the differences between the .223 Remington and the United States Military’s 5.56mm NATO.
Although some may say that the overall differences are only within the powder loads, this is sometimes not true.
Often, different ammunition manufacturers such as Winchester, Remington, and Wolf, have a tendency to cut their cartridges at sharper angles than perhaps military contract manufacturers would cut the same caliber round. For example, the US military currently employs what is known as: the SS109 Green Tip. This piece of ammunition is notorious for its ability to blast through armor.
With an armor piercing tip, this projectile is known for its increased velocity, and overall striking power, which are a few of the reasons it is currently being used by the US military. Armor piercing, high velocity rounds, however, are not always the case using commercially purchased ammunition.
As far as which round will work better in your AR-15 rifle, also known as the Colt 6920 Law Enforcement, Military, Government Carbine. It is most suggestible by any member of the armed forces to only use 5.56mm NATO rounds. The reason for that is because the 5.56mm is what is designed to function through the AR-15 weapon system.
Most operators will agree, and also suggest the use of the 5.56mm NATO over the .223 Remington, for the sheer reason and purpose of action and intentional function of the round.
Most AR-15’s are stamped on the receiver 5.56mm NATO, in this case, Marines, Soldiers, and Operators agree that the 62 grain SS109 Green Tip, is the most practical for running in this weapon system.
A positive note for both ammunition choices, is the fact that both are deemed what is called a common round; meaning, that either round can easily be found anywhere and does not need to be special ordered or anything like that.
As far as the .223 Remington is concerned, this round functions well under the ability of the 5.56mm NATO. Based on its decreased velocity and stopping power, due to the lower grain percentage.
The .223 Remington uses about 36 grains per round compared to the 62 grain SS109. Lower grain counts, can result in typical feed errors and weapons malfunction, making the 5.56mm NATO a much better choice.