aluminum gun barrels

primer and acrylic should do fine. but i normally use enamels. just curious, why doesn't your son have his own fsm user name?

I would prime it with a good automotive-type primer. They are designed to adhere to metal, not plastic. Lightly sand the primer smooth and then you can use any type of modeling paint that you want to use on it.

tamiya fine white primer is good with metal. make sure you clean the metal throughly, and yer set.

Yes, first clean the barrel in soap-water and then use a good primer ; as mentioned before the Tamiya primers are good on metal. For the final color, it doesn't matter if you use acrylic or enamel, personally I stay away from acrylic these days, but that's my opinion.