Lucky shot and shield / flak cannon perfect shot

Is lucky shot really possible against shield?
I have never see one for now.

Are you sure for the always hit of the flak cannon?

EDIT: I have done some test:
There is no lucky shot against shield (An 1000 shot/s 100000dmg weapon with 0 penetration can not destroy a shield)
The flak always hit, just something I did wrong ^^’