ΔE 16.6, loose: different enough that you should pick on purpose. Dark Gunmetal is a little lighter, much more muted than Radiant Platinum.
Not as a straight swap; see the closer alternatives below. Loose match (ΔE 17). Dark Gunmetal is a little lighter, much more muted than Radiant Platinum.
The same difference applies the other way round: Radiant Platinum is a little darker, much more saturated.
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 Radiant Platinum on the colour wheel See Dark Gunmetal on the colour wheel
All matches: Radiant Platinum equivalents · Dark Gunmetal equivalents