ΔE 11.5, fair: the same colour family, but not a straight swap. Gunmetal is noticeably darker than Black Ice.
Only where an exact match doesn’t matter, such as a new unit or a highlight. Fair match (ΔE 12). Gunmetal is noticeably darker than Black Ice.
The same difference applies the other way round: Black Ice is noticeably lighter.
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 Ice on the colour wheel See Gunmetal on the colour wheel
All matches: Black Ice equivalents · Gunmetal equivalents