I spend another day sanding.
The primer was used as filler. When long block sanding the surface becomes more smoother than before. Probably 90% or more of the first coat of primer was removed.
The gray areas are high spots, the white low spots. Above you can see one of the holes I filled.
I stopped to grab my black spray paint can. This helps in finding low areas, also. Once all the black is sanded off you are left with a very smooth surface.
Here is the black guide coat.
The 2nd coat of primer was rolled on afterward.
With the tools I have this is the smoothest surface I'll ever get. But still, I sanded after the two coats to follow. More on that later.