The cartridges .223 Remington and 5.56×45mm NATO often get lumped together, but the confusion around them has a long, tangled history. Though they look nearly identical, critical differences in ...

Some believe the 5.56 NATO was the original military cartridge and that the 223 Remington was the civilian offshoot. That’s not the case. In 1970, NATO (North Atlantic Treaty Organization) affiliated ...

For most shooters the difference between .223 Remington and 5.56×45 NATO is minor, but it matters because 5.56 is typically loaded to higher pressures and uses a slightly different chamber leade.