
Some of them do… Or at least, they did - I mostly remember seeing it when I was in high school, and it sort of faded out when I was in college. Not sure if it fell out of style, or if it’s only a thing with the Hot Topic/mall goth crowd
Edit: uncorrected an accidental autocorrect
Their math was flawed, but I’m not really sure how to explain the math part better. I get what they were going for, though.
It’s closer to decimal divisions of an inch, so a .223 caliber bullet would be a hair shy of a quarter of an inch (.25) wide.
Edit: just realized you had the second part of that already