ΔE 7.0, close: similar, with a visible difference side by side. Armageddon Dust is a little lighter, cooler than Light Brown. They are different kinds of paint: AMMO by Mig Light Brown is an opaque base/layer 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.
Usually, if you are not matching paint already on the model. Close match (ΔE 7). Armageddon Dust is a little lighter, cooler than Light Brown. They are different kinds of paint.
The same difference applies the other way round: Light Brown is a little darker, 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 Light Brown on the colour wheel See Armageddon Dust on the colour wheel
All matches: Light Brown equivalents · Armageddon Dust equivalents