Today I did another acrylic spray test and just wanted to pass it on since you asked about acrylic and using Vallejo ( I'm assuming Model Air paint and not Model Color paint) earlier in this thread. I put down a thin single coat of stynylrez primer (very slightly thinned) with a .25 needle set. I've never done that with that fine a needle. I shot it 26 psi and it went on beautiful. That dried overnight. Today I took a fresh bottle of Vallejo model air paint and shot on two coats of that straight from the bottle over the stynylrez primer. I've also never done that totally unthinned with a .25 needle set. It went on great at 25 psi.
Just passing on the info. I know that if I continued to spray a larger area with the Vallejo unthinned with no retarder and that needle, eventually it would have tip dried. But for the sake of a test on a prescription bottle that did not occur.