Burnt Iron vs Gunmetal Blue

How close are they?

ΔE 21.5, loose: different enough that you should pick on purpose. Gunmetal Blue is a little darker, more muted, cooler than Burnt Iron.

Can I use Gunmetal Blue instead of Burnt Iron?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 21). Gunmetal Blue is a little darker, more muted, cooler than Burnt Iron.

Can I use Burnt Iron instead of Gunmetal Blue?

The same difference applies the other way round: Burnt Iron is a little lighter, more saturated, 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.