An old painter named Ray in Bakersfield taught me to feather my primer coats by feel, not by eye
Honestly I still think about this one guy I met about 4 years back at a shop off Chester Ave in Bakersfield. His name was Ray, he had been spraying cars since the 70s, and I was maybe a year into doing body work and thought I knew it all. He came over while I was priming a quarter panel and asked why I was stopping the coat at the tape line. I said that's where the panel ends, and he just laughed and said "son, primer don't stop at no line, it fades." Then he took my gun and showed me how to overlap each pass and let the last couple coats get thinner so the edge just melts into the metal. Took him like 2 minutes and I had been fighting sanding scratches at that seam for a whole day. Ngl it saved me so many comebacks after that, because a hard edge in primer always shows up later under the base. Anybody else here get taught something like that by an old timer who barely said 10 words the whole time?
Old Ray knew what he was doing. Feathering the primer is the whole game, a hard tape line will ghost through your base coat every single time. I learned the same thing from a guy named Manny back in the 90s and it cut my comebacks in half. Two minutes of watching him work taught me more than a year of guessing.