ΔE 25.3, loose: different enough that you should pick on purpose. Rusty Metal is a little darker, much more saturated than Light Gun Metal.
Not as a straight swap; see the closer alternatives below. Loose match (ΔE 25). Rusty Metal is a little darker, much more saturated than Light Gun Metal.
The same difference applies the other way round: Light Gun Metal is a little lighter, much more muted.
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 Light Gun Metal on the colour wheel See Rusty Metal on the colour wheel
All matches: Light Gun Metal equivalents · Rusty Metal equivalents