two bone ik can't fixed left hand location

please see this screenshot.

Animation

i create socket for left hand ik on weapon.

and, get socket location in animation blueprint at event blurprint update animation.

after that, i use two bone ik for left hand ik using rifle’s socket location.

it work’s barely fine, but not perfectly fixed location.

how can i fix it? is this approachs are wrong?

best regards.

image