One of the Vietnam vet groups I belong to on FB shared these pictures. I learned something I didn’t know tonight. The door gunner said he would often do this to avoid the risk of empty cases flying into the tail rotor. I had never heard of this or heard of this before.
As you can see the door gunner has his M60 upside down to “aim” the ejected brass and links away from the direction of the tail rotor when leaning out to fire at targets at certain angles.
I’m not sure if this had the added benefit of making it easier on the gun to cycle the belt or harder. Hopefully Kirk will offer some insight on this.