ΔE 16.2, loose: different enough that you should pick on purpose. Olive Green is noticeably lighter, cooler than Gangrene.
Not as a straight swap; see the closer alternatives below. Loose match (ΔE 16). Olive Green is noticeably lighter, cooler than Gangrene.
The same difference applies the other way round: Gangrene is noticeably darker, 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 Gangrene on the colour wheel See Olive Green on the colour wheel
All matches: Gangrene equivalents · Olive Green equivalents