ΔE 20.6, loose: different enough that you should pick on purpose. Copper Coin is noticeably darker, more saturated, warmer than Skullcrusher Brass.
Not as a straight swap; see the closer alternatives below. Loose match (ΔE 21). Copper Coin is noticeably darker, more saturated, warmer than Skullcrusher Brass.
The same difference applies the other way round: Skullcrusher Brass is noticeably lighter, more muted, 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 Copper Coin on the colour wheel
All matches: Skullcrusher Brass equivalents · Copper Coin equivalents