ΔE 20.6, loose: different enough that you should pick on purpose. Wasteland Brown is noticeably lighter, much more saturated than Shadow Black.
Not as a straight swap; see the closer alternatives below. Loose match (ΔE 21). Wasteland Brown is noticeably lighter, much more saturated than Shadow Black.
The same difference applies the other way round: Shadow Black is noticeably darker, much more muted.
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 Shadow Black on the colour wheel See Wasteland Brown on the colour wheel
All matches: Shadow Black equivalents · Wasteland Brown equivalents