ΔE 22.0, loose: different enough that you should pick on purpose. Ancient Copper is a little lighter, much more muted, warmer than Nebula Copper.
Not as a straight swap; see the closer alternatives below. Loose match (ΔE 22). Ancient Copper is a little lighter, much more muted, warmer than Nebula Copper.
The same difference applies the other way round: Nebula Copper is a little darker, much 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 Nebula Copper on the colour wheel See Ancient Copper on the colour wheel
All matches: Nebula Copper equivalents · Ancient Copper equivalents