ΔE 10.1, fair: the same colour family, but not a straight swap. Armageddon Dust is a little darker, cooler than Matt Grime. They are different kinds of paint: AMMO by Mig Matt Grime is an ink, glaze or transparent paint and Citadel Armageddon Dust is a technical paint or medium, so they won’t behave the same on the model even where the colour is close.
Only where an exact match doesn’t matter, such as a new unit or a highlight. Fair match (ΔE 10). Armageddon Dust is a little darker, cooler than Matt Grime. They are different kinds of paint.
The same difference applies the other way round: Matt Grime is a little lighter, warmer.
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 Matt Grime on the colour wheel See Armageddon Dust on the colour wheel
All matches: Matt Grime equivalents · Armageddon Dust equivalents