How to properly rotate child bone to world space target?

Hi ! I i’m fairly new to UE.
I trying to add rotation to my own modeled tank.
I wrote code that allow to rotate tank’s head
but i can’t to understand why my code do not rotate weapon properly if I’ve rotate my tank by Z axis (timeline 0:19)

here my video

here is code about Aiming Tank to target

here is Tank model *.blend (112 KB)

any help about this? thx!