Model master gloss paints, what PSI?

Just like Grandpa wore, that's a big "Depends"!

Here's MusicCity's take on it.

I know people who spray at settings supposedly too low for airbrushes to work well, and they put out wonderful paint jobs.

I know people who spray at ridiculously high settings, and their work is amazing.

As near as I can tell there is a pretty much universal rule to start at, though:

Gravity Fed: thin paints to the consistency of 2% milk and shoot between 10-20psi.

Siphon Fed: thin paints to the consistency of 2% milk and shoot between 15-25psi.

The very best advice I can give you is to get a cheap model and practice, practice, practice. Do some experiments and keep notes on your thinning ratio and air pressure.

Oh. And practice!