I'm getting varied results. Aiming when the ship is turning is fine, as the gun continues to rotate to keep you on target - you fire and because the ship is turning the round seems to come out almost sideways.
I expect shots to inherit momentum (10+ years of Tribes means I have a rather good understanding of the physics involved), but you try firing flak from any turning ship!
If you have a frame of reference (the front of a Goldfishes balloon, as the main Goldfish gunner as an example) then you can adjust to compensate. You know the ship is turning, you can manually adjust. If you have no frame of reference, such as a lower gun on a turning Junker when firing broadside, then I wish you the best of luck with your hail-mary shots.
I know communication is key with this, and I know most captains will try to keep it steady. However, with things as they are, ships like the Pyramidion and Goldfish are a little more.. user friendly, as you will be pointing your nose at the target, whereas a Junker will often circle to keep guns to bear, endlessly turning and ruining gunner's aims.
My two cents.