ΔE 20.9, loose: different enough that you should pick on purpose. Crimson Magenta is a little darker, much more saturated, warmer than Shell Shocked.
Not as a straight swap; see the closer alternatives below. Loose match (ΔE 21). Crimson Magenta is a little darker, much more saturated, warmer than Shell Shocked.
The same difference applies the other way round: Shell Shocked is a little lighter, much more muted, cooler.
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 Shell Shocked on the colour wheel See Crimson Magenta on the colour wheel
All matches: Shell Shocked equivalents · Crimson Magenta equivalents