Crousader:
Various good advice given already in this thread but I want to revisit a particular topic. You commented that you understand the idea that you have to aim where the bandit will be. However you stated the following as well:
I typically fly planes with nose mounted gun packages, I get well within range (inside D400) I get on the guys six , put him in the middle of my pipper and squeeze.
I bolded the key phrase for emphasis. Putting the bandit in the middle of your pipper is not aiming and shooting where the bandit is going to be. Assuming the bandit is turning you are already shooting behind the bandit if you're centering the bandit in your pipper.
Let me second Spatula's post. Don't let it get lost. Andy Bush's articles on SimHq are the best ones I have seen on the topic. The last thread Spatula posted is Andy's most concise gunnery article on the topic. Here is the link again for it:
http://www.simhq.com/_air/air_031b.htmlSo back to where to put the bandit in relationship to your pipper. Andy does a great job laying out rules of thumb for it. Here's an example worth briefly discussing..

Source: Andy Bush, SimHQ - "Air to Air Gunnery Revisited"
Notice just how far away the bandit is in relationship to the pipper. The bandit is not anywhere near centered in the pipper because we have to aim and shoot at where the bandit is going to be. This is "leading" the bandit.
Andy talks about using the concept of bandit wingspan distances for lead. There is a whole theory around this that Andy elaborates on. Here the pipper is placed about 3 wingspan distance ahead of the bandit as visually measured from the pipper to the bandit (the pipper and bandit in the same 2D plane) from inside the shooter's cockpit.
In this specific example the amount of lead used here at 3 wingspans is based on the amount of angle-off of the target's tail the shooter is in relation to the target. The greater the angle-off, the greater the lead, the further out ahead of the target's flight path the pipper needs to be placed. The following illustration show's where the center of the pipper would be placed at 1, 2, or 3 wingspans away from the target demonstrating this idea.

Source: Andy Bush, SimHQ - "Air to Air Gunnery Revisited"
The general equation for lead is:
L = Vt x 1000 x sin(angle_off) / Vm
L = amount of lead (mils)
Vt = target velocity (ft/s)
angle_off = angle_off target (degrees)
Vm = average muzzle velocity of the round from firing to impact including your velocity (ft/s)
We mentioned angle_off already above but increasing Vt also means you have to shoot with more lead as well. In other words if a target was at the same angle_off but travelling at a higher speed than you would need to have to shoot with more lead than would have been the case at a slower speed but the same angle_off.
There are other factors to keep in mind as well: gravity, dispersion, projectile weight etc. but hopefully that whet's your appetite to go study up on Andy's articles

. Just one particular note- Andy talks about designing gunsights from AH. That was done for an older version of AH so not sure what parts of his talk there still apply or not.
SHOOTING FROM DEAD 6One comment I think worth mentioning since people keep bringing it up- On shooting from dead-six, there's a factor that complicates the shooting dead-six that a lot folks don't realize and that's the concept of vertical convergence. Gravity pulls bullets down so guns are actually are set at some angle so that bullets arrive in the center of your pipper (if you were just shooting while flying level) at the convergence distance you desire. The following is a pic showing a sideview elevation of bullet trajectory for vertical convergence:

Source: Andy Bush, SimHQ - "Air to Air Gunnery Revisited"
In this pic, the gun has been set for convergence at about 300 yards. The implication of this vertical convergence is that if the target is less than 300 yards than the bullet stream in relationship to the pipper is actually below the center point of the pipper at less than 300 yards. The closer the target is, the lower the bullet stream is below the center of your pipper. Therefore if your target is closer than your gun convergence then you will need to put the center of your pipper above your target to hit it.
Here is a short .WMV that I did to illustrate the point (guns set at 300 yds convergence on a P-51D). Note where the bullet impacts are in relationship to the gunsite depending on how close the target is to my plane. The closer the target, the lower beneath the center of the pipper the bullets hit.
http://brauncomustangs.org/films/gunrange.wmv Hope that's helpful!
Tango, XO
412th FS Braunco Mustangs