ΔE 15.1, loose: different enough that you should pick on purpose. Ancient Copper is noticeably lighter, more muted than Iridescent Copper Light (Coarse). They are different kinds of paint: Golden Iridescent Copper Light (Coarse) is a pearl paint and Vallejo Ancient Copper is a metallic, so they won’t behave the same on the model even where the colour is close.
Not as a straight swap; see the closer alternatives below. Loose match (ΔE 15). Ancient Copper is noticeably lighter, more muted than Iridescent Copper Light (Coarse). They are different kinds of paint.
The same difference applies the other way round: Iridescent Copper Light (Coarse) is noticeably darker, more saturated.
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 Iridescent Copper Light (Coarse) on the colour wheel See Ancient Copper on the colour wheel
All matches: Iridescent Copper Light (Coarse) equivalents · Ancient Copper equivalents