actually some of the finest builders you will see online roll primer on their projects. go to rcsb and look for projects done by sevarg or monocoupe, their talents are indescribable. they both roll their primer on, you are going to sand most of it off anyway. and it's a lot faster way to fill in pinholes, etc. the foam rollers at lowe's (key word: foam) are available in the 3-4" range. with that you can roll your primer so thin you can see through it. all techniques have their advantages, even rattle cans of filler primer; they are quick and convenient. good luck.