ΔE 15.7, loose: different enough that you should pick on purpose. Ancient Copper is a little lighter, more muted, warmer than Overlord Brass.
Not as a straight swap; see the closer alternatives below. Loose match (ΔE 16). Ancient Copper is a little lighter, more muted, warmer than Overlord Brass.
The same difference applies the other way round: Overlord Brass is a little 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 Overlord Brass on the colour wheel See Ancient Copper on the colour wheel
All matches: Overlord Brass equivalents · Ancient Copper equivalents