7.62
But you wouldnt want to be on the wrong end of it.
http://www.youtube.com/watch?v=ARp1UAIQUGU

Want.

Throw your axe away http://www.youtube.com/watch?v=QC8jnSaCqxY&feature=related

A-10 uber gun

they had the gatling on discovery the other day, 3000 rounds per minute! It hummed rather than rattled