Why a gun at all?
Newer UAV are carrying Hellfires, can carry the SDB, and there’s even a laser-guided 2.75” rocket now available.
Carrying a heavy gun with tons of dumb munitions is counterproductive for that kind of work. Especially when it requires the UAV to orient and close in with the target. Hellfires and rockets don’t.
When you have troops in contact, the gun is the better choice.
I attended a briefing a few months ago where an A-10 pilot told how he and his wingman stopped an ambush against an Army convoy. They used only the gun.