Math was never my strong point in life but some of this metric stuff is confusing to me an ignorant old man! A 8mm mauser bore is .3106. Ok I get that. Now a 8.15x46 is bore .2992! I assumed this 8.15 would be the 8mm of .3106 plus 15. But according to the book a 8.15 is bore of .2992! I know they are right and I am confused. Any body willing to explain this to me? Go slow!