ΔE 8.2, close: similar, with a visible difference side by side. Gun Metal is a little darker than Leadbelcher.
Usually, if you are not matching paint already on the model. Close match (ΔE 8). Gun Metal is a little darker than Leadbelcher.
The same difference applies the other way round: Leadbelcher is a little lighter.
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 Leadbelcher on the colour wheel See Gun Metal on the colour wheel
All matches: Leadbelcher equivalents · Gun Metal equivalents