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

Paul Harrell has a great video on YouTube going into great detail about different caliber origins.

If you like firearms, he’s awesome. [Here’s the video if you’re curious.](https://youtu.be/_zrH8nn0kAc)