ΔE 8.8, close: similar, with a visible difference side by side. Russ. AF Grey Blue is a little lighter, more saturated than Ash Grey.
Usually, if you are not matching paint already on the model. Close match (ΔE 9). Russ. AF Grey Blue is a little lighter, more saturated than Ash Grey.
The same difference applies the other way round: Ash Grey is a little darker, 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 Ash Grey on the colour wheel See Russ. AF Grey Blue on the colour wheel
All matches: Ash Grey equivalents · Russ. AF Grey Blue equivalents