ΔE 33.3, loose: different enough that you should pick on purpose. Graphite Grey is noticeably darker, much more muted than Militarum Green.
Not as a straight swap; see the closer alternatives below. Loose match (ΔE 33). Graphite Grey is noticeably darker, much more muted than Militarum Green.
The same difference applies the other way round: Militarum Green is noticeably lighter, much 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 Militarum Green on the colour wheel See Graphite Grey on the colour wheel
All matches: Militarum Green equivalents · Graphite Grey equivalents