remember that it is a model that for me is a form of art , we try to copy the reality but you can't always do what really happens in reality, a tank is metal covered by the primer that protects from rust and a substrate suitable for painting ,we can do this on plastic, Plastic/ primer / paint, but in the case of a metallic finish you can't, you can't (except with the bare-metal-foil but is another story) cover the plastic with metal, so you have to find a system to deceive the eye and make it believe it is real metal and it is understood that with a black gloss primer the effect comes much better than with the traditional primer, however as mentioned before this technique is used much more in the airplanes that on AFV and other and certain products work well with both gloss and matt, others need gloss because they are designed specifically to be used with that ... we reproduce reality we don't copy it
go and see how much work is done by those who build aircraft in Bare Metal before and after painting, and you will be amazed by the work behind it, preparation of the plastic, primer, polishing primer, paint, buff the paint ..... especially with the Alcad II paints