I have assembled my blaster, and need some tips on how to paint it!

In some pics it looks dark grey, in other it looks like gun metal grey, and in some it looks black with a lot of dirt. What colour should I use as a base, and how should I continue from there?

I have done a dark grey base coat, but I'm not happy with it. Maybe it's just because it's too shiny, I'm not sure.

Help would be much appreciated!