ΔE 8.3, close: similar, with a visible difference side by side. Obsidian Black is a little darker, more muted than Tinmetal Grey.
Usually, if you are not matching paint already on the model. Close match (ΔE 8). Obsidian Black is a little darker, more muted than Tinmetal Grey.
The same difference applies the other way round: Tinmetal Grey is a little lighter, 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 Tinmetal Grey on the colour wheel See Obsidian Black on the colour wheel
All matches: Tinmetal Grey equivalents · Obsidian Black equivalents