Red Copper vs Forged Red

How close are they?

ΔE 22.6, loose: different enough that you should pick on purpose. Forged Red is a little darker, much more saturated, cooler than Red Copper.

Can I use Forged Red instead of Red Copper?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 23). Forged Red is a little darker, much more saturated, cooler than Red Copper.

Can I use Red Copper instead of Forged Red?

The same difference applies the other way round: Red Copper is a little lighter, much more muted, warmer.

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.