Polished Silver vs Gunmetal Grey

How close are they?

ΔE 6.9, close: similar, with a visible difference side by side. Gunmetal Grey is a little lighter, more saturated than Polished Silver.

Can I use Gunmetal Grey instead of Polished Silver?

Usually, if you are not matching paint already on the model. Close match (ΔE 7). Gunmetal Grey is a little lighter, more saturated than Polished Silver.

Can I use Polished Silver instead of Gunmetal Grey?

The same difference applies the other way round: Polished Silver is a little darker, 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.