ΔE 30.8, loose: different enough that you should pick on purpose. Brass is noticeably darker, much more saturated than Pig Iron.
Not as a straight swap; see the closer alternatives below. Loose match (ΔE 31). Brass is noticeably darker, much more saturated than Pig Iron.
The same difference applies the other way round: Pig Iron is noticeably 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 Pig Iron on the colour wheel See Brass on the colour wheel
All matches: Pig Iron equivalents · Brass equivalents