ΔE 12.6, fair: the same colour family, but not a straight swap. Ancient Copper is much more muted than Gladius Bronze.
Only where an exact match doesn’t matter, such as a new unit or a highlight. Fair match (ΔE 13). Ancient Copper is much more muted than Gladius Bronze.
The same difference applies the other way round: Gladius Bronze is 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 Gladius Bronze on the colour wheel See Ancient Copper on the colour wheel
All matches: Gladius Bronze equivalents · Ancient Copper equivalents