ΔE 6.4, close: similar, with a visible difference side by side. Bright Neutral Grey is a little lighter than Longbeard Grey.
Usually, if you are not matching paint already on the model. Close match (ΔE 6). Bright Neutral Grey is a little lighter than Longbeard Grey.
The same difference applies the other way round: Longbeard Grey is a little darker.
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 Longbeard Grey on the colour wheel See Bright Neutral Grey on the colour wheel
All matches: Longbeard Grey equivalents · Bright Neutral Grey equivalents