ΔE 13.4, fair: the same colour family, but not a straight swap. Semi Gloss Bright Gun Metal is noticeably lighter, more saturated than Gun Metal.
Only where an exact match doesn’t matter, such as a new unit or a highlight. Fair match (ΔE 13). Semi Gloss Bright Gun Metal is noticeably lighter, more saturated than Gun Metal.
The same difference applies the other way round: Gun Metal is noticeably darker, 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.
See Gun Metal on the colour wheel See Semi Gloss Bright Gun Metal on the colour wheel
All matches: Gun Metal equivalents · Semi Gloss Bright Gun Metal equivalents