ΔE 15.9, loose: different enough that you should pick on purpose. Red Brown is a little darker, cooler than Steel Legion Drab.
Not as a straight swap; see the closer alternatives below. Loose match (ΔE 16). Red Brown is a little darker, cooler than Steel Legion Drab.
The same difference applies the other way round: Steel Legion Drab is a little lighter, 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 Steel Legion Drab on the colour wheel See Red Brown on the colour wheel
All matches: Steel Legion Drab equivalents · Red Brown equivalents