ΔE 6.1, close: similar, with a visible difference side by side. USA Flat Brown is a little lighter, cooler than Bosh Chestnut.
Usually, if you are not matching paint already on the model. Close match (ΔE 6). USA Flat Brown is a little lighter, cooler than Bosh Chestnut.
The same difference applies the other way round: Bosh Chestnut is a little darker, warmer.
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 Bosh Chestnut on the colour wheel See USA Flat Brown on the colour wheel
All matches: Bosh Chestnut equivalents · USA Flat Brown equivalents