Every part of a paint gun is different, with different sizes, different geometries, different complexities, etc. Additionally, coatings may have different properties (and costs). That's why it's important to dial in the gun pattern so you get a good job of painting your parts without wasting material. No two jobs are exactly alike. So there is no "one size fits all" setting from job to job and material to material.
Most Spray Guns have different knobs and dials, each controlling a different aspect in terms of the style and amount of material being sprayed. Looking at them can be confusing at first, but with a little practice, you'll be able to successfully add patterns to your particular job at hand. Here are the basic controls that come with most Spray Guns:
Round/Wide Shot Adjustment Control: This setting usually appears as a knob on the gun body and is available if your gun is equipped with a wide-blast air cap (the one with the "horns" on it). This knob only controls the amount of air flowing through those horns in the air cap. The more air that flows through, the wider the spray pattern. The less air that passes through, the smoother the spray pattern.
Atomizing Air Control: This setting is also usually shown as a knob on the gun body (see your gun manual to determine which knobs do what). This knob controls the atomizing air, or "primary air," that flows into the gun. If you turn this setting off completely, no air will flow through the gun and you'll just have solid paint coming out of the nozzle. Use this setting to balance the amount of atomization desired with the amount of overspray produced. More atomization usually means more spraying.
Material Flow Adjustment: This setting is usually shown as a knob near the back of the gun body and behind the needle. It controls how far the needle retracts from the nozzle when the gun is triggered. This controls how much material is allowed to flow out of the nozzle. This is a fine tuned setting, but since the primary control of material flow is determined by the needle/nozzle size on the gun itself. Normally, it is set to fully open, but it can be turned off if desired.
