Gun Metal vs Iridescent Bronze (Fine)

How close are they?

ΔE 27.6, loose: different enough that you should pick on purpose. Iridescent Bronze (Fine) is noticeably lighter, much more saturated than Gun Metal. They are different kinds of paint: Army Painter Gun Metal is a metallic and Golden Iridescent Bronze (Fine) is a pearl paint, so they won’t behave the same on the model even where the colour is close.

Can I use Iridescent Bronze (Fine) instead of Gun Metal?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 28). Iridescent Bronze (Fine) is noticeably lighter, much more saturated than Gun Metal. They are different kinds of paint.

Can I use Gun Metal instead of Iridescent Bronze (Fine)?

The same difference applies the other way round: Gun Metal is noticeably darker, much more muted.

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.