ΔE 15.8, loose: different enough that you should pick on purpose. Russian AF Blue is noticeably darker, more muted than Ducat Blue.
Not as a straight swap; see the closer alternatives below. Loose match (ΔE 16). Russian AF Blue is noticeably darker, more muted than Ducat Blue.
The same difference applies the other way round: Ducat Blue is noticeably lighter, 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 Ducat Blue on the colour wheel See Russian AF Blue on the colour wheel
All matches: Ducat Blue equivalents · Russian AF Blue equivalents