Sturdy vs Steel Bullet

[Shen]

Does Cobalion EX's Steel Bullet get past BCR Crustle's Sturdy Ability? As in, would Crustle's HP become 10 or would it be KO'd?

 

[PokePop]

One has nothing to do with the other. There is no interaction.
Cobalion does its full damage.
Then, if when KO's are checked for, Crustle would be KO'd, Sturdy kicks in and reduces the damage on it so that it is not KO'd.

That happens after Steel Bullet has already placed all of it's damage.