ΔE 22.1, loose: different enough that you should pick on purpose. Spartan Bronze is noticeably darker, much more muted than Castellax Bronze.
Not as a straight swap; see the closer alternatives below. Loose match (ΔE 22). Spartan Bronze is noticeably darker, much more muted than Castellax Bronze.
The same difference applies the other way round: Castellax Bronze is noticeably lighter, 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 Castellax Bronze on the colour wheel See Spartan Bronze on the colour wheel
All matches: Castellax Bronze equivalents · Spartan Bronze equivalents