ok well all the devilbliss hvlp and non hvlp's that i have at work have tips like 93p or 068 my sata at home has a 1.4 and i woudl never never put primer in it on the tip is too small you should have a gun thats just for primer as you said this one is for yes you can over reduce the primer but that breaks it down and makes it not work as good. and why shriwin williams? guess if your going cheap your better off with a ppg product or RM product but to go cheaper omni by ppg has a primer that you use out of the can mp281 i think is the new number and you jsut reduce it with lac thinner. but yes the 1.4 tip is way to small to spray primer for whats its intended to do. which is help level imperfections. my experence is i been in body and paint for over 10 years and now i work at christensen shipyard as a painter painting 30 mill. dollar yachts.