ΔE 10.0, close: similar, with a visible difference side by side. Sons of Horus Green is a little darker, more muted than Majestic Fortress.
Usually, if you are not matching paint already on the model. Close match (ΔE 10). Sons of Horus Green is a little darker, more muted than Majestic Fortress.
The same difference applies the other way round: Majestic Fortress is a little lighter, 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 Majestic Fortress on the colour wheel See Sons of Horus Green on the colour wheel
All matches: Majestic Fortress equivalents · Sons of Horus Green equivalents