By coincidence I happen to currently know two separate guys who were, or claim to have been, snipers in the military. I never even thought to question their claims until the issue of bullet caliber came up. At the cafe where I hang out what is meant by bullet caliber was raised during a conversation. I was pretty sure, though not certain, it was a measurement of diameter, but someone else disputed that. It occurred to me the ex-sniper who hangs out there should be able to settle it, so I went and asked him. His hesitant answer was that he was fairly sure caliber was a measurement of bullet length. When I got home I consulted the wikipedia and found he was wrong. A few days later I started telling this story to the other ex-sniper I happen to know at a different cafe, and before I'd finished the story he interrupted me to say that caliber was a measure of bullet length. Caliber, is, in fact, a measurement of bullet diameter: both "snipers" were wrong. Of course one needn't know what caliber means to be a good enough shot to be a sniper, but it strikes me that this is a little too basic for an authentic sniper to be ignorant about. They're both nice guys, and don't speak of their military past with any particularly boastful tone, so I wonder how much weight I should give this gap in knowledge.