The neck gauge thickness is different between the two. Look closer. .251 vs .253.
0.002 inches? 0.05 mm? That could be just wear and tear on the resizing die.
Maybe I’m a fool, but I’ve always used 5.56 and .223 brass interchangeably. And I’ve never noticed any difference in accuracy with the different brass and the same powder charge and bullet.
I’d be interested in hearing the experience of other reloaders. Or people who may have been reloaders before their unfortunate canoeing accidents.