How to tell if 30 Luger or 9mm Luger
 

This gets asked a lot, never occurred to me to just take pictures.

The 'check'

Take a normal sized, old fashioned pencil and drop it down the bore. If its farily tight, its 30 Luger (aka 7.65mm Luger) - if it falls easily and there is plenty of room, its 9mm!!

A Simple Way To Tell 7.65mm Or 9mm~~~
 

If it fits it is 7.65mm,

Ed, excellent clear example & pics. If you dont have a pencil handy, another way is to look at the width of the sight base relative to the bore. The 9mm bore is distinctly wider than the sight base; with the .30 it is just a little wider.
John