I served in an ADA unit in Germanyin the mid 80's. Among the systems our battalion fielded was the M163-VADS. 20 mm Vulcan mounted to an M-113 chassis. In the 80's at least it had range-only radar. The German government wouldn't let us live fire them over land so we had to railhead them up to the North Sea coast to shoot over water. Sounds like an incredibly loud wet burp. A piece of that brass gets down the front of your shirt you're gonna know it! Death to helicopters if undetected, useless pretty much against fixed wing. That was the skinny from the gunners anyway.