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

In Engineering and Science, precision is important. The more decimal digits are specified, the tighter the tolerance must be when manufacturing., plus or minus half the lowest digit. So whether 5.56mm or 6.00mm, but never 6mm.

A 6mm would be 5.5mm to 6.5mm

A 6.0mm would be 5.95mm to 6.05mm

A 6.00mm would be 5.995 to 6.005mm

And that sort of precision is required to keep the bullet the right size for the barrel.