Bison-Beast vs Longbeard Grey

How close are they?

ΔE 17.1, loose: different enough that you should pick on purpose. Longbeard Grey is a little lighter, much more muted than Bison-Beast.

Can I use Longbeard Grey instead of Bison-Beast?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 17). Longbeard Grey is a little lighter, much more muted than Bison-Beast.

Can I use Bison-Beast instead of Longbeard Grey?

The same difference applies the other way round: Bison-Beast is a little darker, 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.