ΔE 9.9, close: similar, with a visible difference side by side. Heavy Metal is a little darker, more muted than Black Metal.
Usually, if you are not matching paint already on the model. Close match (ΔE 10). Heavy Metal is a little darker, more muted than Black Metal.
The same difference applies the other way round: Black Metal is a little lighter, more saturated.
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.
See Black Metal on the colour wheel See Heavy Metal on the colour wheel
All matches: Black Metal equivalents · Heavy Metal equivalents