I used to live probably 12 or so miles as the crow flies from Lake City Ammunition Plant. On a clear day and with the right atmospheric weather conditions you could hear the buzz from them performing these ammunition tests. The gun set up in the video may or may not be from Lake City, but I can tell you the Buzz when that thing rips off a string is impressive to be heard 12 or more miles away.
My jaw dropped when I first asked one of the firefighters what that buzz was I kept hearing and they said it was a Gatling Gun from Lake City Ammo Plant. I said, you're kidding me and then several of them said, "Oh, no... That's a 30 mm Gatling Gun from an A-10 Warthog. They make the ammo for them there!"