First off, practice off line against the drones, work on shots from the front, front quarter, and side profiles from each of their aircraft. Do this for about 30 minutes solid and you will begin to see a difference, also, check your convergence settings and post them here.
This may sound strange, but when I shoot, I almost see the enemy move in slow motion and it helps my aim. I tend to take alot of impossible shots so my gunnery % isn't too hot, but the end result is quite favorable. Don't worry about gun %, it is just a stat... after a time you will feel the proper distance. For example, yesterday, I took a snap shot on a Corsair that was 800+ out while he was in a full bank turn away from me at high speed, less than a 1 second burst killed him. Turns out I got lucky and I hit his cockpit. If you're worried about accuracy %, you wouldn't even bother making that shot.
One last bit of advice, stick to one aircraft. Swapping around won't help you learn gunnery (as most of them have different guns with different nose/wing placement) or the characteristics of that particular aircraft.