ΔE 10.8, fair: the same colour family, but not a straight swap. Barrel Grey is a little darker, more muted than Dark Rust.
Only where an exact match doesn’t matter, such as a new unit or a highlight. Fair match (ΔE 11). Barrel Grey is a little darker, more muted than Dark Rust.
The same difference applies the other way round: Dark Rust is a little lighter, more saturated.
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 Dark Rust on the colour wheel See Barrel Grey on the colour wheel
All matches: Dark Rust equivalents · Barrel Grey equivalents