I've found that leading the target is necessary, if he's moving left to right I have to aim to the right so the shell arrives when he does. There's also a momentum built in, firing on either beam while running at high speed means the shell travels forward while going out to the side. I doubled the muzzle velocity in the cannon's .sim file, not sure if it makes a difference or not. Using this mod;
http://www.subsim.com/radioroom/down...do=file&id=666
it's easier to see the actual trajectory.