Gun Chrome vs Dark Gunmetal

How close are they?

ΔE 6.7, close: similar, with a visible difference side by side. Dark Gunmetal is a little lighter, more muted than Gun Chrome.

Can I use Dark Gunmetal instead of Gun Chrome?

Usually, if you are not matching paint already on the model. Close match (ΔE 7). Dark Gunmetal is a little lighter, more muted than Gun Chrome.

Can I use Gun Chrome instead of Dark Gunmetal?

The same difference applies the other way round: Gun Chrome is a little darker, more saturated.

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.