Every handgun and rifle caliber is legal, from .22 Long Rifle up to the monster .95 caliber. Types of those bullets may be illegal, such as armor piercing or explosive. But there are legal variants of all calibers.
The differences are minimal, but important to keep in mind.
The 5.56x45mm NATO is the military version of the .223 Remington cartridge. The NATO round has more energy in it (higher pressures), and I believe it is shaped VERY slightly differently to where it requires a barely-longer chamber.
That is why it is important to purchase a rifle with a 5.56 or .223 "Wylde" chamber if you wish to have the largest selection of ammo. Rifles chambered for .223 Remington ONLY are not safe for constant use of the hotter 5.56 cartridge.
The 5.56x45mm NATO is the military version of the .223 Remington cartridge. The NATO round has more energy in it (higher pressures), and I believe it is shaped VERY slightly differently to where it requires a barely-longer chamber.
That is why it is important to purchase a rifle with a 5.56 or .223 "Wylde" chamber if you wish to have the largest selection of ammo. Rifles chambered for .223 Remington ONLY are not safe for constant use of the hotter 5.56 cartridge.
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