ΔE 11.0, fair: the same colour family, but not a straight swap. Forged Red is noticeably lighter than Iridescent Copper (Coarse). They are different kinds of paint: Golden Iridescent Copper (Coarse) is a pearl paint and Vallejo Forged Red is a metallic, so they won’t behave the same on the model even where the colour is close.
Only where an exact match doesn’t matter, such as a new unit or a highlight. Fair match (ΔE 11). Forged Red is noticeably lighter than Iridescent Copper (Coarse). They are different kinds of paint.
The same difference applies the other way round: Iridescent Copper (Coarse) is noticeably darker.
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 (Coarse) on the colour wheel See Forged Red on the colour wheel
All matches: Iridescent Copper (Coarse) equivalents · Forged Red equivalents