Some funky codes.

Variables RElev and RHeading point to the target selected in the cockpit frame, see this example turret. Mounted weapons need to be 800-muzzle velocity guns.

The firing lead is calculated in the 20+ variables, so xml editing is more convenient when adding this to your own turret.

This example turret can typically shoot down medium sized planes 2 km away. Note this turret can only point up so fly below your target. Btw, I found the gun firing indicator in the game is incorrect, it seem to fail considering the velocity of gun projectiles are relative to the cockpit's translational velocity... simplist proof is when you fly with the tanker side by side it points to a bit front of the tanker, but you have to shoot right at the tanker to hit it...