A Remington 223 charges about 55,000 psi: the second and most crucial difference between the two is that a 5.56 NATO chamber has a .125″ neck length. This allows a 5.56 NATO cartridge to hold approximately one more granular powder; This gives you higher performance than your 223 Remington Cousin.
223 What is the name of the cartridge?
The cartridge is known as the “M193 5.56mm Ball Cartridge” in the US military. The 5.56×45mm NATO 223 was also made by Remington. The development of the cartridge, 223 Remington reloading dies which eventually became the 223 Remington, was associated with developing a new lightweight combat rifle.