Charles Gunst's "Enemy Coast Ahead" and "ECA Control Panel" improve gun velocity. So does Hakan Langebro's ECA Online (which is understandable since Hakan used Charles Gunst's gun data for ECAO!). Also, Mosi developed a German Gun Patch for EAW that also increases the velocity to realistic standards for Luftwaffe aircraft, if I'm not mistaken.

[...in a maneuver I frequently can't even see the tracers...]

Are you trying to fire while pulling positive G's? Remember, if you are using the Realistic Gunnery setting in EAW, then the rounds you fire will be influenced by the G-forces that your plane is being subjected to. If you are in a tight, high-G turn when you fire, your machine gun bullets or cannon shells will not travel straight ahead, but will instead have a curving flight path.....curving back under your nose! The more G you pull, the more pronounced the effect becomes. This is a fact that real pilots had to deal with. The best way to shoot is to straighten out and pull no G at all. This ensures that your fire will travel relatively straight ahead. If you try to fire while maneuvering, you will have a very difficult time getting your rounds on target. The best thing to do is try to haul your nose in front of the target and then straighten out for a shot. If you must fire while in a maneuver (after all, the enemy might not want to cooperate long enough for you to get a straight shot!), try to get as close as possible before firing. This increases your chances of hitting the target.