ΔE 16.0, loose: different enough that you should pick on purpose. Ancient Copper is noticeably lighter, more saturated, warmer than Brass.
Not as a straight swap; see the closer alternatives below. Loose match (ΔE 16). Ancient Copper is noticeably lighter, more saturated, warmer than Brass.
The same difference applies the other way round: Brass is noticeably darker, 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 Brass on the colour wheel See Ancient Copper on the colour wheel
All matches: Brass equivalents · Ancient Copper equivalents