I am confused on what we are measuring, like I know a .45 is larger then a .40... and the.40 is larger then the 9mm but the bullet is not 31 times smaller. I know I should know this by this point in my gun collecting time, but it has slipped by me. I know how the calibers line up a 22 to a 22 mag to what a 25? then to the 380 to the 9 to the 40 to the 45 and a few in between. But what does it all mean?