ΔE 23.5, loose: different enough that you should pick on purpose. Rusty Metal is noticeably lighter, more saturated than Metallic Black.
Not as a straight swap; see the closer alternatives below. Loose match (ΔE 23). Rusty Metal is noticeably lighter, more saturated than Metallic Black.
The same difference applies the other way round: Metallic Black is noticeably darker, 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.
See Metallic Black on the colour wheel See Rusty Metal on the colour wheel
All matches: Metallic Black equivalents · Rusty Metal equivalents