Hello, I'm an expert in firearms and ballistics. It's important to note that while the .223 Remington and 5.56x45mm NATO cartridges are often used interchangeably, they are not identical and there are technical differences between them.

The .223 Remington was originally designed as a civilian cartridge, while the 5.56x45mm NATO was developed for military use. The key difference lies in the chamber and throat length specifications. A rifle chambered in .223 Remington may not safely handle the higher pressure of the 5.56x45mm NATO rounds. However, a rifle chambered for 5.56x45mm NATO can safely fire .223 Remington ammunition.

Using .223 Remington rounds in a rifle chambered for 5.56x45mm NATO is generally safe, but the reverse is not recommended due to the potential for increased pressure causing damage or injury. Always follow the manufacturer's guidelines for your specific firearm.

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If you purchase factory ammo, your .556 NATO ammo may be loaded hotter than sporting .223 ammo. Yes. As others have said, guns chambered in 5.56 can safely shoot .223, but not vice-versa. ... I believe the exception I know of is my Ruger Mini-14 Ranch rifle , although not marked for 5.56 can shoot either .223 OR 5.56.read more >>