I read on the Nisha-Subforum about the possible synergy between the Plunkett and Crack Shot and gave it a try.
But instead of procing Crack Shot on the first shot with a full magazin on a crit, it instead simply killed the enemies. The sound effekt of the skill was present.
Instead, the explosion triggers if i have one bullet missing from the magazin. For example:
My Plunkett has 11 bullets. I shot a guy in the head, next shot on the ground and kill him afterwards with 10 bullets in the mag and the explosion triggers.
If I figure out how to link videos, I have one recorded where I show this process
Thank you @VaultHunter101