ΔE 23.8, loose: different enough that you should pick on purpose. AMT-7 Greyish Blue is noticeably lighter, more saturated, cooler than Greatcoat Grey.
Not as a straight swap; see the closer alternatives below. Loose match (ΔE 24). AMT-7 Greyish Blue is noticeably lighter, more saturated, cooler than Greatcoat Grey.
The same difference applies the other way round: Greatcoat Grey is noticeably darker, more muted, 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 Greatcoat Grey on the colour wheel See AMT-7 Greyish Blue on the colour wheel
All matches: Greatcoat Grey equivalents · AMT-7 Greyish Blue equivalents