ΔE 30.2, loose: different enough that you should pick on purpose. Ironbreaker is noticeably darker than Light Metal.
Can I use Ironbreaker instead of Light Metal?
Not as a straight swap; see the closer alternatives below. Loose match (ΔE 30). Ironbreaker is noticeably darker than Light Metal.
Can I use Light Metal instead of Ironbreaker?
The same difference applies the other way round: Light Metal is noticeably 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.