Black Metal vs Gunmetal

How close are they?

ΔE 7.3, close: similar, with a visible difference side by side. Gunmetal is a little darker, more saturated than Black Metal.

Can I use Gunmetal instead of Black Metal?

Usually, if you are not matching paint already on the model. Close match (ΔE 7). Gunmetal is a little darker, more saturated than Black Metal.

Can I use Black Metal instead of Gunmetal?

The same difference applies the other way round: Black Metal is a little lighter, more muted.

ΔE is the colour difference between our two swatch estimates: under about 6 is close, over about 15 is loose. Real paints also differ in finish, coverage and how they thin, so test before you commit.