The metallic paint is not like a standard paint. It contains metal flake that "lays" a certain way depending upon how much air pressure you have on the gun as well as the speed and stroke direction of the gun, the angle of the gun to the surface, and the distance it is from the car as you paint.
Each of these can be challenging on their own, but the cumulative difficulty is much higher still when compared to a regular paint.
The clear-coat will add a visual depth as well as provide great protection, but it will NOT make a poorly applied metallic paint look uniform.
Start with a spare piece of metal, something with curves and angles is even better since it more closely patterns the complex shapes you will be painting on the real thing.
