ΔE 13.3, fair: the same colour family, but not a straight swap. Medium Sea Grey is noticeably lighter than Hell Bent for Leather.
Only where an exact match doesn’t matter, such as a new unit or a highlight. Fair match (ΔE 13). Medium Sea Grey is noticeably lighter than Hell Bent for Leather.
The same difference applies the other way round: Hell Bent for Leather is noticeably darker.
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 Hell Bent for Leather on the colour wheel See Medium Sea Grey on the colour wheel
All matches: Hell Bent for Leather equivalents · Medium Sea Grey equivalents