ΔE 6.9, close: similar, with a visible difference side by side. Dark Gunmetal is a little lighter than Runefang Steel.
Usually, if you are not matching paint already on the model. Close match (ΔE 7). Dark Gunmetal is a little lighter than Runefang Steel.
The same difference applies the other way round: Runefang Steel is a little darker.
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.
See Runefang Steel on the colour wheel See Dark Gunmetal on the colour wheel
All matches: Runefang Steel equivalents · Dark Gunmetal equivalents