Aguila Blanca
Staff
Another possibility, which might be more durable than the spray enamel paint you can buy in hardware stores, is automotive paint. Most automotive paint today is 2-component polyurethane. I don't know if it is available in Europe but, here in the U.S., we can go to a company that specializes in selling automotive paint and they will mix any colour we want and put it in an aerosol can. It isn't cheap, but the result is more durable than spray enamel, and you don't need any special equipment such as an air brush or spray gun.
If you want to change the barrel to nickel, why not make it nickel? https://www.caswellplating.com/electroplating-anodizing/nickel-plating-kits.html
To get a hard, black finish on the barrel you could also plate it with black chrome ... but that requires a base coat of copper or nickel pating. https://www.caswellplating.com/electroplating-anodizing/black-krome-plating-kits.html
If you want to change the barrel to nickel, why not make it nickel? https://www.caswellplating.com/electroplating-anodizing/nickel-plating-kits.html
To get a hard, black finish on the barrel you could also plate it with black chrome ... but that requires a base coat of copper or nickel pating. https://www.caswellplating.com/electroplating-anodizing/black-krome-plating-kits.html