ΔE 16.5, loose: different enough that you should pick on purpose. Chestnut Brown is noticeably lighter, more muted than Dark Red Tone. They are different kinds of paint: Army Painter Dark Red Tone is a wash/shade and Nocturna Models Chestnut Brown is an opaque base/layer paint, so they won’t behave the same on the model even where the colour is close.
Not as a straight swap; see the closer alternatives below. Loose match (ΔE 16). Chestnut Brown is noticeably lighter, more muted than Dark Red Tone. They are different kinds of paint.
The same difference applies the other way round: Dark Red Tone is noticeably darker, 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 Dark Red Tone on the colour wheel See Chestnut Brown on the colour wheel
All matches: Dark Red Tone equivalents · Chestnut Brown equivalents