Metallic Orange vs Ancient Copper

How close are they?

ΔE 18.5, loose: different enough that you should pick on purpose. Ancient Copper is a little lighter, much more muted than Metallic Orange.

Can I use Ancient Copper instead of Metallic Orange?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 19). Ancient Copper is a little lighter, much more muted than Metallic Orange.

Can I use Metallic Orange instead of Ancient Copper?

The same difference applies the other way round: Metallic Orange is a little darker, much 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.