ΔE 29.2, loose: different enough that you should pick on purpose. Steampunk Copper is noticeably lighter, more muted, warmer than Skullcrusher Brass.
Not as a straight swap; see the closer alternatives below. Loose match (ΔE 29). Steampunk Copper is noticeably lighter, more muted, warmer than Skullcrusher Brass.
The same difference applies the other way round: Skullcrusher Brass is noticeably darker, more saturated, cooler.
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 Skullcrusher Brass on the colour wheel See Steampunk Copper on the colour wheel
All matches: Skullcrusher Brass equivalents · Steampunk Copper equivalents