From: Flight Image of the Day
30mm may not sound like a very big number, but it’s all about the context. For instance, a 30mm gap, that’s quite bridgeable. But a 30mm bullet hole, well then it becomes a big number. Here, from user flyvertosset on AirSpace, is the business end of a Fairchild Republic A-10, showing its General Electric GAU-8/A Avenger 30mm cannon.