A few years ago a Kansas farmer bought a hanger on an abandoned Army air field. It was kinda sorta locked, and distant from towns, and chock full of “junk”. Upon getting into it and cleaning the junk out for a couple days, they discovered a fully functioning 20mm anti aircraft gun mounted on a 4 wheel trailer, along with multiple cases of good ammo. They towed it down to a nearby NG Armory and surrendered it to the shock of the Sergeant that ran the joint.
This story smells. I recall the duster had a 40 mm set.