ΔE 10.0, close: similar, with a visible difference side by side. Hammered Copper is a little darker, more saturated than Mithril.
Usually, if you are not matching paint already on the model. Close match (ΔE 10). Hammered Copper is a little darker, more saturated than Mithril.
The same difference applies the other way round: Mithril is a little lighter, more muted.
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 Mithril on the colour wheel See Hammered Copper on the colour wheel
All matches: Mithril equivalents · Hammered Copper equivalents