Leadbelcher vs Blackened Steel

How close are they?

ΔE 6.6, close: similar, with a visible difference side by side. Blackened Steel is a little darker than Leadbelcher.

Can I use Blackened Steel instead of Leadbelcher?

Usually, if you are not matching paint already on the model. Close match (ΔE 7). Blackened Steel is a little darker than Leadbelcher.

Can I use Leadbelcher instead of Blackened Steel?

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.