Coppery Orange vs Rusty Metal

How close are they?

ΔE 21.6, loose: different enough that you should pick on purpose. Rusty Metal is noticeably lighter, warmer than Coppery Orange.

Can I use Rusty Metal instead of Coppery Orange?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 22). Rusty Metal is noticeably lighter, warmer than Coppery Orange.

Can I use Coppery Orange instead of Rusty Metal?

The same difference applies the other way round: Coppery Orange is noticeably darker, 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.