Oh, it must be a typo. I found a more official source and it says, bullet diameter = 9.27mm, case length = 38.7mm, cartridge length = 56mm, rim diameter/case head diameter = 11.35mm, bullet weight = 16.0 grams, powder charge = 0.5 grams, muzzle velocity = 310 meters per second. This is for SP-5 and isn't perfect eiither. I am going to go through the military ammunition manual and see if I can get some more exact figures. These are just rounded off figures for a non-technical book.