As I have mentioned in other links about this... What I have REALLY Come to rely on is "EPOXY, STAINLESS STEEL APPLIANCE PAINT" for a "Metallic Base Coat"
I've used this on my DV Chest and Belt Boxes and it works GREAT! AND it's EXTREMELY Durable to wear!
This is VERY Important when you do the Main "Color Coat" and want to do the "Paint Chip Effects" and get that "Bare/Exposed Metal" look!
I First lightly sand and clean the piece to be painted. Then I spray 3 to 4 coats of the "Epoxy Paint", letting each layer dry thoroughly BEFORE the next coat.
Once those are done, I don't even worry about sanding it. I just first add the "Chip Effect Agent" like Liquid Latex or "Mustard" as a barrier between the "Metal" and the "Main Color{s} Coats. I usually spray One or Two of this coat to get a good, opaque Effect.
Then, Rub off the Latex or Mustard and... WHA-LA! Perfect and Accurate "Paint Chip Weathering/Wear" Effect!
If you do various "Thicknesses" of the "Barrier Agent" {i.e. Latex or Mustard} then you can achieve the look of either "HEAVY CHIPPING" or "Gradual/Faded" Paint wear.
If anyone has any questions about all of this, PLEASE feel free to ask. I am VERY Glad to help in any way I can!
Also there are TONS of Tutorials on this kind of stuff on YouTube if you look! "Smugglers Room" has done a Complete Tutorial on building a "Resin/3D Printed Blaster Kit".
Again, anyone needing help, Please feel free to message me.
Good Luck.
Joe