ΔE 7.7, close: similar, with a visible difference side by side. AMT-12 Dark Grey is a little lighter, more muted than Steel Shadow.
Usually, if you are not matching paint already on the model. Close match (ΔE 8). AMT-12 Dark Grey is a little lighter, more muted than Steel Shadow.
The same difference applies the other way round: Steel Shadow 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.
See Steel Shadow on the colour wheel See AMT-12 Dark Grey on the colour wheel
All matches: Steel Shadow equivalents · AMT-12 Dark Grey equivalents