When I asked for 9mm, the kid behind the counter asked me what that translated to in inches. Confused by his question (not thinking someone who sells guns could be that stupid) I asked him what he meant. His response "All of these appear to be written in inches .40, .45, .22. I don't see any that have the metric conversion written on them."
http://www.youtube.com/watch?v=DY67XaX6oM8