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