ΔE 14.1, fair: the same colour family, but not a straight swap. Gunmetal Blue is noticeably lighter, more saturated than Metallic Black.
Only where an exact match doesn’t matter, such as a new unit or a highlight. Fair match (ΔE 14). Gunmetal Blue 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 Gunmetal Blue on the colour wheel
All matches: Metallic Black equivalents · Gunmetal Blue equivalents