The GAU-8 30mm Gatling gun, home of the Brrrt.
It's darned impressive up close.
Yes, those barrels are rifled, and the rifling on this cannon in particular was nice and sharp.
The GAU-8 is attached of course to the most impressive air-ground aircraft yet built, the A-10.
It's a very cool aircraft to walk around and the GAU-8 certainly is an attraction all by itself.
Sadly, the A-10 was static display only (with tons of people constantly crowding around it, forget about a shot taking in the entire aircraft) this time and did not take to the air, which would have been awesome.