ΔE 6.6, close: similar, with a visible difference side by side. Russian Green 4BO is a little lighter than Dark Drab.
Usually, if you are not matching paint already on the model. Close match (ΔE 7). Russian Green 4BO is a little lighter than Dark Drab.
The same difference applies the other way round: Dark Drab 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 Dark Drab on the colour wheel See Russian Green 4BO on the colour wheel
All matches: Dark Drab equivalents · Russian Green 4BO equivalents