ΔE 10.6, fair: the same colour family, but not a straight swap. Rusty Metal is a little lighter than Heavy Armour.
Only where an exact match doesn’t matter, such as a new unit or a highlight. Fair match (ΔE 11). Rusty Metal is a little lighter than Heavy Armour.
The same difference applies the other way round: Heavy Armour 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 Heavy Armour on the colour wheel See Rusty Metal on the colour wheel
All matches: Heavy Armour equivalents · Rusty Metal equivalents