You can send it to a body shop and for a small fee they can do a reverse electrolysis and strip all the chrome and nickel off.
www.acmeplating.com did my M4
I don't recommend sanding...
Before you spray you need to clean the brass with acetone or alcohol.
Then spray on a self etching primer or the paint won't stick to the brass.
Then spray on a light tack coating of paint. Let it dry completely.
Repeat with another coat of paint.
Bake it, but don't burn it.
Fill the engravings with a paint stick (from Micro-tools)
Let it settle for a day or so and then reassemble.
Remember, you're going to get better results with several thin coats of paint, instead of one thick one.
Use an airbrush with a moisture trap, instead of a can.
Experiment with paint dilutions first on a scrap surface that has a primer coat.
Use a fine grain enamel paint as sold by Micro-tools.
If you rush this it will look like hell and chip off.