They seem very easily damaged by GV mounted weapons and seem to be the first to go regardless of the hit location. The right cannon seems particularly afflicted.
I caught a burst in my left wing, and lost my right cannnon.
On a different sortie, I got a single ping resulting in a hole in my windscreen and lost my right cannon.
I attacked a Panzer with the rockets and got a few pings to the cocpit (he fired when I was nose on and I saw the bullet holes in my windscreen) resulting in both cannons being damaged.
