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

Some are. There are both [6mm](https://en.wikipedia.org/wiki/6_mm_caliber) and [8mm](https://en.wikipedia.org/wiki/7.92%C3%9757mm_Mauser) bullets, loaded into a variety of cartridges. Cartridge and projectile design is complicated, with each iteration designed to perform in a specific way and fill a specific niche.