This may well be the coolest gun EVER! The Barrett XM109 25MM Payload Rifle. This thing is a man-portable 25mm anti-tank … semiauto rifle. You could theoretically shoot thirty rounds a minute with this thing, if you could get around the fact that your shoulder would be somewhere near your ass, and reloading the pair of five shot clips three times in that minute. Bastards Inc. has a bit more info (and some hilarious comments from the users) on the gun.