At AEDC, an Air Force test site with wind tunnels & also one facility which has what they call the "Gun Range. In this range, they fire various projectiles through a large underground tube. At one location in the facility, they have several photos of projectiles in flight showing the Shock waves from them, very interesting. These all stated at what velocity they had been fired.
Beside these pictures, someone had hung an old rusty cast iron skillet with a hole in the bottom. A notation beneath it read 12 ga slug at 30 yds.
