Primer as paint?

Yes I have.  I use red oxide primer for red oxide painted ship hulls, and have used gray primer for other hulls.  And, for small parts representing bare steel, I will spray with a flat dark gray primer and then dry brush a faint silver patina.  Makes a very nice steel finish.

Me too. Never a problem.

I don't see a thing wrong with it Mark

In fact, I can think of a couple of great reasons to try and make it work out that way on purpose

One reason is that "modern modelers" are quite famous for trying to cover with as few coats of paint as possible, to preserve the detail molded into the kit,,,,,,,,,if you find a primer that is the correct color, you get the best of both worlds

There are a couple of model paint acrylic primers that fall right into being FS spec colors,,,,,but, my favorite is using a White as the primer on '60's USN aircraft,,,,when it is all primered and ready for the color coat, I only have to paint the Gray parts and go on from there,,,,,,any Red, Yellow or Orange parts also already have the White undercoat they need

Ya know, I can remember a time (50+ years ago) when a lot of us who were in high school and could afford a car (gas 25 cents a gallon and a nice running 1950 Ford 2 door was maybe $100) painted and operated our vehicles with a coat of either flat gray or flat black primer.  (seems we all had plans to eventually paint the things  either in a candy color or a metalflake color but just couldn't seem to get there)

hah, I remember those days,,,,,one of my Cougars was black primer and still had the "post dent" in the left hind quarter from when I bought it to "fix up and paint"

the Engine, Trans, Wheels, Brakes, rear end,,,,,,,,all of the moving parts were New or rebuilt and repainted, though

heck, the seats were torn in places, but, the engine hoses never got old,,,,,,,,,I think it was because we could work on them anywhere we could park them, but, it took a special place to paint them up

hmm, drats,,,,,,,plastic modeling is not all that different, it seems

Rex

I built a '53 Chevy street rod for a contest and painted the flat black primer on. It got to be the night before the contest and I didn't have time to finish the paint job. I took it to the contest and it took 3rd place. So evidently the judges didn't have a problem with it.

Jim