Why are bullet sizes usually in decimal and not just a whole number?

Question

For example, why 5.56mm and not just 6mm? Why 7.62mm instead of just 8?

In: Technology

Answer 1

Ok so the simple answer here is that there are just too many incompatible cartridges to not have more numbers available. If you rounded everything close to 8 to 8 then you’d have many cartridges that wouldn’t fit or be dangerous in the wrong gun all called 8.

I can’t think of any off the top of my head but some cartridges were “misnamed” from their actual bullet diameter because that number was already taken and the goal was to avoid confusion.