ΔE 9.8, close: similar, with a visible difference side by side. Blue Black is a little darker, more saturated than Ironclad Grey.
Usually, if you are not matching paint already on the model. Close match (ΔE 10). Blue Black is a little darker, more saturated than Ironclad Grey.
The same difference applies the other way round: Ironclad Grey is a little lighter, 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.
See Ironclad Grey on the colour wheel See Blue Black on the colour wheel
All matches: Ironclad Grey equivalents · Blue Black equivalents