ΔE 8.6, close: similar, with a visible difference side by side. Sepia is a little darker, warmer than Rifle Brown.
Usually, if you are not matching paint already on the model. Close match (ΔE 9). Sepia is a little darker, warmer than Rifle Brown.
The same difference applies the other way round: Rifle Brown is a little lighter, cooler.
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 Rifle Brown on the colour wheel See Sepia on the colour wheel
All matches: Rifle Brown equivalents · Sepia equivalents