ΔE 5.5, very close: most people won’t see a difference side by side. Grim Black is a little lighter, more muted than 3B AU/ZB AU. They are different kinds of paint: AK Interactive 3B AU/ZB AU is an opaque base/layer paint and Army Painter Grim Black is a one-coat contrast-style paint, so they won’t behave the same on the model even where the colour is close.
Yes, for most jobs. Very close match (ΔE 5). Grim Black is a little lighter, more muted than 3B AU/ZB AU. They are different kinds of paint.
The same difference applies the other way round: 3B AU/ZB AU is a little 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 3B AU/ZB AU on the colour wheel See Grim Black on the colour wheel
All matches: 3B AU/ZB AU equivalents · Grim Black equivalents