Tinmetal Grey vs Dark Gunmetal

How close are they?

ΔE 6.7, close: similar, with a visible difference side by side. Dark Gunmetal is more muted than Tinmetal Grey.

Can I use Dark Gunmetal instead of Tinmetal Grey?

Usually, if you are not matching paint already on the model. Close match (ΔE 7). Dark Gunmetal is more muted than Tinmetal Grey.

Can I use Tinmetal Grey instead of Dark Gunmetal?

The same difference applies the other way round: Tinmetal Grey is 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.