Despite books about air war in WW2 mention quite often direct hits by flak on B-17s/B-24s leading to an explosion of the bomb load, i am not aware of any pilot claims of explicitly shooting at the pay load.
Having the much closer combat ranges of irl in mind, going for the payload would have been suicide as the attacking fighter might have been caught by the explosion blast. German night fighters aimed for wing fuel tanks due to this whilst attacking with Schraege Musik. You will also might heard of the issues of RAF pilots avoiding to get killed/damaged whilst intercepting V-1s.
All i remember are very rare claims of 262 pilots scoring kills by hitting the bomb load - with 30mm and/or R4Ms but i looks like that those were just lucky hits and a result of their tactics of using high speed zoom climbs from below and behind.
To be complete, even it was not shooting at the payload:
We have the Knoke memoirs claiming that he scored 3 B-17 kills with a single SC 250 dropped with his 109 from 1.0000 meters above with a fuze delay.
He claims he scored a direct hit on the middle plane of these 3 B-17s, the explosion of the bomb load of the middle plane caused the 2 subsequent kills.


