Iron Wolf vs Bismark's Grave

How close are they?

ΔE 7.7, close: similar, with a visible difference side by side. Bismark's Grave is more saturated, warmer than Iron Wolf.

Can I use Bismark's Grave instead of Iron Wolf?

Usually, if you are not matching paint already on the model. Close match (ΔE 8). Bismark's Grave is more saturated, warmer than Iron Wolf.

Can I use Iron Wolf instead of Bismark's Grave?

The same difference applies the other way round: Iron Wolf is more muted, cooler.

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.