Gun Metal vs Royal Burgundy

How close are they?

ΔE 31.5, loose: different enough that you should pick on purpose. Royal Burgundy is a little darker, much more saturated than Gun Metal.

Can I use Royal Burgundy instead of Gun Metal?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 32). Royal Burgundy is a little darker, much more saturated than Gun Metal.

Can I use Gun Metal instead of Royal Burgundy?

The same difference applies the other way round: Gun Metal is a little 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.