ΔE 22.7, loose: different enough that you should pick on purpose. Hydra Turquoise is a little lighter, much more saturated than Semi Gloss Bright Gun Metal.
Not as a straight swap; see the closer alternatives below. Loose match (ΔE 23). Hydra Turquoise is a little lighter, much more saturated than Semi Gloss Bright Gun Metal.
The same difference applies the other way round: Semi Gloss Bright Gun Metal 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.
See Semi Gloss Bright Gun Metal on the colour wheel See Hydra Turquoise on the colour wheel
All matches: Semi Gloss Bright Gun Metal equivalents · Hydra Turquoise equivalents