ΔE 16.7, loose: different enough that you should pick on purpose. Battledress Brown is noticeably lighter, more saturated than Black Templar.
Not as a straight swap; see the closer alternatives below. Loose match (ΔE 17). Battledress Brown is noticeably lighter, more saturated than Black Templar.
The same difference applies the other way round: Black Templar is noticeably darker, 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 Black Templar on the colour wheel See Battledress Brown on the colour wheel
All matches: Black Templar equivalents · Battledress Brown equivalents