Battlefield Brown vs Dark Red

How close are they?

ΔE 22.8, loose: different enough that you should pick on purpose. Dark Red is a little lighter, much more saturated than Battlefield Brown.

Can I use Dark Red instead of Battlefield Brown?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 23). Dark Red is a little lighter, much more saturated than Battlefield Brown.

Can I use Battlefield Brown instead of Dark Red?

The same difference applies the other way round: Battlefield Brown is a little darker, 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.