You need to clear coat after you paint. Use automotive clear (Rustoleum rattle can is fine).
Spray one light coat, wait 15-20min.
Spray second coat heavy, wait 20 min.
Spray third coat real heavy but even.
If the gun is too shiny when it dries, go over it with steel wool. If it gets too dull, all you have to do is wax it like a car.
That paint will never scratch with clear coat.
"For the High and Exalted One who lives forever, whose name is Holy says this: 'I live in a high and holy place, and with the oppressed and lowly of spirit, to revive the spirit of the lowly and revive the heart of the oppressed." - Isaiah57:15